diff --git a/MathKit/MathKit.h b/MathKit/MathKit.h
index 3d7494c..c9831f9 100644
--- a/MathKit/MathKit.h
+++ b/MathKit/MathKit.h
@@ -10,10 +10,38 @@
 #import "MPExpressionElement.h"
 #import "NSString+MPExpressionElement.h"
 #import "MPFunction.h"
+#import "MPSuffixFunction.h"
+
 #import "MPSumFunction.h"
+#import "MPParenthesisFunction.h"
+#import "MPPowerFunction.h"
+#import "MPFractionFunction.h"
+#import "MPRootFunction.h"
+
+#import "MPToken.h"
+#import "MPFunction+MPToken.h"
+#import "MPTokenStream.h"
+
+#import "MPExpressionTreeElement.h"
+#import "MPExpressionTree.h"
+#import "MPSummand.h"
+#import "MPOperatorChain.h"
+#import "MPProduct.h"
+#import "MPFactor.h"
+#import "MPValueGroup.h"
+#import "MPNumber.h"
+#import "MPVariable.h"
+#import "MPFunction+MPValue.h"
+#import "MPFunctionValue.h"
+#import "MPUnexpectedSymbolValue.h"
+#import "MPFactorial.h"
+
+#import "MPEvaluationContext.h"
+#import "MPMathRules.h"
 
 #import "MPRangePath.h"
-#import "MPException.h"
 #import "NSIndexPath+MPAdditions.h"
+#import "NSRegularExpression+MPParsingAdditions.h"
+
 #import "MPExpressionView.h"
 #import "MPExpressionStorage.h"
\ No newline at end of file
diff --git a/MathPad.xcodeproj/project.pbxproj b/MathPad.xcodeproj/project.pbxproj
index af7869b..dafd4a9 100644
--- a/MathPad.xcodeproj/project.pbxproj
+++ b/MathPad.xcodeproj/project.pbxproj
@@ -76,7 +76,6 @@
 		3B85833919BB63C500D76A8D /* MPExpressionElement.h in Headers */ = {isa = PBXBuildFile; fileRef = 3BFAC3961997B67400B3EF67 /* MPExpressionElement.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		3B85833A19BB63D400D76A8D /* MPFunction.h in Headers */ = {isa = PBXBuildFile; fileRef = 3B87E35E19009D5F00259938 /* MPFunction.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		3B85834119BB651E00D76A8D /* MPRangePath.h in Headers */ = {isa = PBXBuildFile; fileRef = 3B87E35B1900933200259938 /* MPRangePath.h */; settings = {ATTRIBUTES = (Public, ); }; };
-		3B85834219BB652900D76A8D /* MPException.h in Headers */ = {isa = PBXBuildFile; fileRef = 3B0F69A719028BC600817707 /* MPException.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		3B85834319BB653700D76A8D /* MPSumFunction.h in Headers */ = {isa = PBXBuildFile; fileRef = 3BB09EC71906FD830080A5ED /* MPSumFunction.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		3B85834419BB654D00D76A8D /* NSString+MPExpressionElement.h in Headers */ = {isa = PBXBuildFile; fileRef = 3BFAC39A1997BC7600B3EF67 /* NSString+MPExpressionElement.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		3B85834519BB655200D76A8D /* NSIndexPath+MPAdditions.h in Headers */ = {isa = PBXBuildFile; fileRef = 3BB09EDC190728220080A5ED /* NSIndexPath+MPAdditions.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -94,7 +93,6 @@
 		3BBEA93619BB79A700133766 /* MPFunction.m in Sources */ = {isa = PBXBuildFile; fileRef = 3B87E35F19009D5F00259938 /* MPFunction.m */; };
 		3BBEA93A19BB79A700133766 /* MPSumFunction.m in Sources */ = {isa = PBXBuildFile; fileRef = 3BB09EC81906FD830080A5ED /* MPSumFunction.m */; };
 		3BBEA93B19BB79A700133766 /* MPRangePath.m in Sources */ = {isa = PBXBuildFile; fileRef = 3B87E35C1900933200259938 /* MPRangePath.m */; };
-		3BBEA93C19BB79A700133766 /* MPException.m in Sources */ = {isa = PBXBuildFile; fileRef = 3B0F69A819028C6000817707 /* MPException.m */; };
 		3BBEA93D19BB79A700133766 /* NSString+MPExpressionElement.m in Sources */ = {isa = PBXBuildFile; fileRef = 3BFAC39B1997BC7600B3EF67 /* NSString+MPExpressionElement.m */; };
 		3BBEA93E19BB79A700133766 /* NSIndexPath+MPAdditions.m in Sources */ = {isa = PBXBuildFile; fileRef = 3BB09EDD190728220080A5ED /* NSIndexPath+MPAdditions.m */; };
 		3BBEA93F19BB79A700133766 /* MPExpressionView.m in Sources */ = {isa = PBXBuildFile; fileRef = 3B87E3551900856F00259938 /* MPExpressionView.m */; };
@@ -162,8 +160,6 @@
 /* End PBXCopyFilesBuildPhase section */
 
 /* Begin PBXFileReference section */
-		3B0F69A719028BC600817707 /* MPException.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = MPException.h; sourceTree = "<group>"; };
-		3B0F69A819028C6000817707 /* MPException.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPException.m; sourceTree = "<group>"; };
 		3B0F69AB1902A82C00817707 /* MPExpressionTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = MPExpressionTests.m; path = ../MathPadTests/MPExpressionTests.m; sourceTree = "<group>"; };
 		3B3A4AAC19F71855001E9D54 /* MPRootFunction.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MPRootFunction.h; sourceTree = "<group>"; };
 		3B3A4AAD19F71855001E9D54 /* MPRootFunction.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPRootFunction.m; sourceTree = "<group>"; };
@@ -427,6 +423,7 @@
 			isa = PBXGroup;
 			children = (
 				3BC46B4B19B38CB60033F13A /* Base Expression Classes */,
+				3B69B68219E6E8A50028E608 /* Expression Tree */,
 				3BB09EBC1905EF210080A5ED /* Functions */,
 				3BC46B4C19B38CD20033F13A /* Independant Classes */,
 				3BC46B4D19B38CFB0033F13A /* Helpers */,
@@ -515,6 +512,8 @@
 				3BFAC38D1997B61300B3EF67 /* MPExpression.h */,
 				3BFAC38E1997B61300B3EF67 /* MPExpression.m */,
 				3BFAC3961997B67400B3EF67 /* MPExpressionElement.h */,
+				3BFAC39A1997BC7600B3EF67 /* NSString+MPExpressionElement.h */,
+				3BFAC39B1997BC7600B3EF67 /* NSString+MPExpressionElement.m */,
 				3B87E35E19009D5F00259938 /* MPFunction.h */,
 				3B87E35F19009D5F00259938 /* MPFunction.m */,
 				3B69B6B719E935E20028E608 /* MPSuffixFunction.h */,
@@ -527,7 +526,6 @@
 				3B7B3A5319CC50B1005849E5 /* MPFunction+MPToken.m */,
 				3BB18AA319CDB3A900986DA0 /* MPTokenStream.h */,
 				3BB18AA419CDB3A900986DA0 /* MPTokenStream.m */,
-				3B69B68219E6E8A50028E608 /* Expression Tree */,
 				3BC46B4F19B506F20033F13A /* Evaluation */,
 			);
 			name = "Base Expression Classes";
@@ -538,8 +536,6 @@
 			children = (
 				3B87E35B1900933200259938 /* MPRangePath.h */,
 				3B87E35C1900933200259938 /* MPRangePath.m */,
-				3B0F69A719028BC600817707 /* MPException.h */,
-				3B0F69A819028C6000817707 /* MPException.m */,
 			);
 			name = "Independant Classes";
 			sourceTree = "<group>";
@@ -547,8 +543,6 @@
 		3BC46B4D19B38CFB0033F13A /* Helpers */ = {
 			isa = PBXGroup;
 			children = (
-				3BFAC39A1997BC7600B3EF67 /* NSString+MPExpressionElement.h */,
-				3BFAC39B1997BC7600B3EF67 /* NSString+MPExpressionElement.m */,
 				3BB09EDC190728220080A5ED /* NSIndexPath+MPAdditions.h */,
 				3BB09EDD190728220080A5ED /* NSIndexPath+MPAdditions.m */,
 				3B52CEDA19BEE63000CEDCFC /* NSRegularExpression+MPParsingAdditions.h */,
@@ -682,7 +676,6 @@
 				3B85834319BB653700D76A8D /* MPSumFunction.h in Headers */,
 				3B85834119BB651E00D76A8D /* MPRangePath.h in Headers */,
 				3B69B6C119E953590028E608 /* MPFactorial.h in Headers */,
-				3B85834219BB652900D76A8D /* MPException.h in Headers */,
 				3B69B69D19E6F2110028E608 /* MPNumber.h in Headers */,
 				3B85834519BB655200D76A8D /* NSIndexPath+MPAdditions.h in Headers */,
 				3B5FF73B19DB2FF500C8348A /* MPPowerFunction.h in Headers */,
@@ -905,7 +898,6 @@
 				3BBEA93E19BB79A700133766 /* NSIndexPath+MPAdditions.m in Sources */,
 				3B52CEDD19BEE63000CEDCFC /* NSRegularExpression+MPParsingAdditions.m in Sources */,
 				3B69B67D19E4915E0028E608 /* MPFractionFunction.m in Sources */,
-				3BBEA93C19BB79A700133766 /* MPException.m in Sources */,
 				3B69B68E19E6EB0D0028E608 /* MPProduct.m in Sources */,
 				3B69B6B619E88E750028E608 /* MPUnexpectedSymbolValue.m in Sources */,
 				3BF59AFF19D80ECC00E54292 /* MPFunctionsViewController.m in Sources */,
diff --git a/MathPad/MPEvaluationContext.h b/MathPad/MPEvaluationContext.h
index 2fb4e91..82119b3 100644
--- a/MathPad/MPEvaluationContext.h
+++ b/MathPad/MPEvaluationContext.h
@@ -6,7 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
+@class MPEvaluationContext;
 
 @interface MPEvaluationContext : NSObject
 
diff --git a/MathPad/MPException.h b/MathPad/MPException.h
deleted file mode 100644
index 8e9346b..0000000
--- a/MathPad/MPException.h
+++ /dev/null
@@ -1,15 +0,0 @@
-//
-//  MPException.h
-//  MathPad
-//
-//  Created by Kim Wittenburg on 19.04.14.
-//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
-//
-
-#ifndef MathPad_MPException_h
-#define MathPad_MPException_h
-
-FOUNDATION_EXPORT NSString *MPIllegalElementException;
-FOUNDATION_EXPORT NSString *MPIllegalElementExceptionElementKey;
-
-#endif
diff --git a/MathPad/MPException.m b/MathPad/MPException.m
deleted file mode 100644
index 8c71821..0000000
--- a/MathPad/MPException.m
+++ /dev/null
@@ -1,12 +0,0 @@
-//
-//  MPException.m
-//  MathPad
-//
-//  Created by Kim Wittenburg on 19.04.14.
-//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
-//
-
-#import "MPException.h"
-
-NSString *MPIllegalElementException = @"MPIllegalSymbolException";
-NSString *MPIllegalElementExceptionElementKey = @"MPIllegalSymbolExceptionSymbolKey";
\ No newline at end of file
diff --git a/MathPad/MPExpression.h b/MathPad/MPExpression.h
index d36ef1a..564631f 100644
--- a/MathPad/MPExpression.h
+++ b/MathPad/MPExpression.h
@@ -6,9 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
-#import "NSString+MPExpressionElement.h"
-#import "MPToken.h"
+FOUNDATION_EXPORT NSString *const MPIllegalElementExceptionElementKey;
 
 FOUNDATION_EXPORT NSString *const MPMathKitErrorDomain;
 FOUNDATION_EXPORT NSString *const MPExpressionPathErrorKey;
@@ -36,7 +34,7 @@ typedef NS_ENUM(NSUInteger, MPReferenceFrame) {
 };
 
 @class MPExpression, MPFunction, MPRangePath, MPExpressionTree, MPExpressionEvaluator;
-@protocol MPExpressionElement;
+@protocol MPExpressionElement, MPToken;
 
 /*!
     @class      MPExpression
diff --git a/MathPad/MPExpression.m b/MathPad/MPExpression.m
index 5848f9f..b98c1f3 100644
--- a/MathPad/MPExpression.m
+++ b/MathPad/MPExpression.m
@@ -7,17 +7,20 @@
 //
 
 #import "MPExpression.h"
+
+#import "MPExpressionElement.h"
 #import "MPFunction.h"
+
 #import "MPRangePath.h"
 
-#import "NSIndexPath+MPAdditions.h"
-#import "MPException.h"
-
 #import "MPExpressionTokenizer.h"
+#import "MPTokenStream.h"
 #import "MPToken.h"
-
 #import "MPExpressionTree.h"
 
+#import "NSIndexPath+MPAdditions.h"
+
+NSString *const MPIllegalElementExceptionElementKey = @"MPIllegalElementExceptionElementKey";
 
 NSString *const MPMathKitErrorDomain = @"MPMathKitErrorDomain";
 NSString *const MPExpressionPathErrorKey = @"MPExpressionPathErrorKey";
@@ -93,7 +96,7 @@ NSString *const MPExpressionPathErrorKey = @"MPExpressionPathErrorKey";
 {
     for (id element in elements) {
         if (![element conformsToProtocol:@protocol(MPExpressionElement)]) {
-            @throw [NSException exceptionWithName:MPIllegalElementException
+            @throw [NSException exceptionWithName:@"MPIllegalElementException"
                                            reason:@"Elements must conform to the MPExpressionElement protocol."
                                          userInfo:@{MPIllegalElementExceptionElementKey: element}];
         }
diff --git a/MathPad/MPExpressionElement.h b/MathPad/MPExpressionElement.h
index 0c5c1af..3ffac4a 100644
--- a/MathPad/MPExpressionElement.h
+++ b/MathPad/MPExpressionElement.h
@@ -6,8 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
-
 @protocol MPExpressionElement <NSObject, NSCopying, NSCoding>
 
 - (BOOL)isString;
diff --git a/MathPad/MPExpressionLayout.h b/MathPad/MPExpressionLayout.h
index 136b93b..8e6a267 100644
--- a/MathPad/MPExpressionLayout.h
+++ b/MathPad/MPExpressionLayout.h
@@ -6,14 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Cocoa;
 #import "MPLayout.h"
-#import "MPExpression.h"
-#import "MPFunctionLayout.h"
 
-#define kMPEmptyBoxWidth (self.usesSmallSize ? 2.0 : 3.0)
-#define kMPEmptyBoxHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font))
-#define kMPEmptyBoxYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)))
+@class MPExpressionLayout, MPExpression, MPFunctionLayout;
 
 @interface MPExpressionLayout : MPLayout
 
diff --git a/MathPad/MPExpressionLayout.m b/MathPad/MPExpressionLayout.m
index 31da0ca..ffbcaa3 100644
--- a/MathPad/MPExpressionLayout.m
+++ b/MathPad/MPExpressionLayout.m
@@ -7,17 +7,16 @@
 //
 
 #import "MPExpressionLayout.h"
-#import "MPFunctionLayout.h"
+
+#import "MPExpression.h"
+#import "MPExpressionElement.h"
 #import "MPPowerFunction.h"
+
+#import "MPFunctionLayout.h"
 #import "MPPowerFunctionLayout.h"
 
-#import "NSString+MPExpressionElement.h"
 #import "NSIndexPath+MPAdditions.h"
 
-#define kMPEmptyBoxDrawingWidth kMPEmptyBoxWidth
-#define kMPEmptyBoxDrawingHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font))
-#define kMPEmptyBoxDrawingYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)/2))
-
 @interface MPExpressionLayout (MPLineGeneration)
 
 - (CTLineRef)lineForElementAtIndex:(NSUInteger)index;
diff --git a/MathPad/MPExpressionStorage.m b/MathPad/MPExpressionStorage.m
index 4ac6403..19def01 100644
--- a/MathPad/MPExpressionStorage.m
+++ b/MathPad/MPExpressionStorage.m
@@ -7,9 +7,11 @@
 //
 
 #import "MPExpressionStorage.h"
+
 #import "MPExpressionView.h"
+#import "MPLayout.h"
 #import "MPExpressionLayout.h"
-#import "MPFunctionLayout.h"
+
 #import "MPRangePath.h"
 
 @interface MPExpressionStorage ()
diff --git a/MathPad/MPExpressionTokenizer.h b/MathPad/MPExpressionTokenizer.h
index e0e3333..0cb064f 100644
--- a/MathPad/MPExpressionTokenizer.h
+++ b/MathPad/MPExpressionTokenizer.h
@@ -6,8 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-#import "MPExpression.h"
+@class MPExpressionTokenizer, MPExpression;
 
 @interface MPExpressionTokenizer : NSObject
 
diff --git a/MathPad/MPExpressionTokenizer.m b/MathPad/MPExpressionTokenizer.m
index 39ad08f..b383f95 100644
--- a/MathPad/MPExpressionTokenizer.m
+++ b/MathPad/MPExpressionTokenizer.m
@@ -7,15 +7,16 @@
 //
 
 #import "MPExpressionTokenizer.h"
+
+#import "MPExpression.h"
+#import "MPExpressionElement.h"
+
 #import "MPToken.h"
-#import "MPFunction+MPToken.h"
 
 #import "NSRegularExpression+MPParsingAdditions.h"
 
-
 #define MPRangeExists(range) (range.location != NSNotFound)
 
-
 @implementation MPExpressionTokenizer
 
 + (NSArray *)tokenizeExpression:(MPExpression *)expression
diff --git a/MathPad/MPExpressionTree.h b/MathPad/MPExpressionTree.h
index 9f011fa..790f76b 100644
--- a/MathPad/MPExpressionTree.h
+++ b/MathPad/MPExpressionTree.h
@@ -6,10 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-#import "MPSummand.h"
 #import "MPExpressionTreeElement.h"
 
+@class MPExpressionTree;
+
 @interface MPExpressionTree : NSObject <MPExpressionTreeElement>
 
 @property (nonatomic, copy) NSString *definedVariable;
diff --git a/MathPad/MPExpressionTree.m b/MathPad/MPExpressionTree.m
index fc458ac..f7bf903 100644
--- a/MathPad/MPExpressionTree.m
+++ b/MathPad/MPExpressionTree.m
@@ -8,6 +8,13 @@
 
 #import "MPExpressionTree.h"
 
+#import "MPSummand.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
+
 @implementation MPExpressionTree {
     NSMutableArray *_summands;
 }
diff --git a/MathPad/MPExpressionTreeElement.h b/MathPad/MPExpressionTreeElement.h
index 8f8b73a..c958f80 100644
--- a/MathPad/MPExpressionTreeElement.h
+++ b/MathPad/MPExpressionTreeElement.h
@@ -6,9 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-#import "MPTokenStream.h"
-#import "MPExpression.h"
+@class MPTokenStream;
 
 @protocol MPExpressionTreeElement <NSObject>
 @required
diff --git a/MathPad/MPExpressionView.h b/MathPad/MPExpressionView.h
index 802ea1a..06c6fa9 100644
--- a/MathPad/MPExpressionView.h
+++ b/MathPad/MPExpressionView.h
@@ -8,8 +8,6 @@
 
 // TODO: Undo/Redo + Delegate
 
-#import <Cocoa/Cocoa.h>
-
 @class MPExpressionView, MPExpressionStorage, MPExpressionLayout, MPRangePath;
 
 @interface MPExpressionView : NSView
diff --git a/MathPad/MPExpressionView.m b/MathPad/MPExpressionView.m
index 3111f42..5edcd89 100644
--- a/MathPad/MPExpressionView.m
+++ b/MathPad/MPExpressionView.m
@@ -7,24 +7,23 @@
 //
 
 #import "MPExpressionView.h"
-#import "MPExpressionStorage.h"
-#import "MPExpressionLayout.h"
-#import "MPFunctionLayout.h"
+
+#import "MPExpression.h"
+#import "MPExpressionElement.h"
 
 #import "MPPowerFunction.h"
+#import "MPParenthesisFunction.h"
 #import "MPFractionFunction.h"
 
 #import "MPRangePath.h"
-
 #import "MPMathRules.h"
-#import "NSIndexPath+MPAdditions.h"
 
-#import "MPSumFunction.h"
-#import "MPParenthesisFunction.h"
-#import "MPParenthesisFunctionLayout.h"
+#import "MPExpressionStorage.h"
+#import "MPExpressionLayout.h"
 
 #import "MPFunctionsViewController.h"
 
+#import "NSIndexPath+MPAdditions.h"
 
 @interface MPExpressionView ()
 
diff --git a/MathPad/MPFactor.h b/MathPad/MPFactor.h
index a471bba..ad016d3 100644
--- a/MathPad/MPFactor.h
+++ b/MathPad/MPFactor.h
@@ -6,10 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPExpressionTreeElement.h"
-#import "MPValueGroup.h"
-#import "MPOperatorChain.h"
+
+@class MPFactor, MPOperatorChain;
+@protocol MPValue;
 
 @interface MPFactor : NSObject <MPExpressionTreeElement>
 
diff --git a/MathPad/MPFactor.m b/MathPad/MPFactor.m
index a9c9cec..cca7b37 100644
--- a/MathPad/MPFactor.m
+++ b/MathPad/MPFactor.m
@@ -7,6 +7,14 @@
 //
 
 #import "MPFactor.h"
+
+#import "MPOperatorChain.h"
+#import "MPValueGroup.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
 #import "MPMathRules.h"
 
 @implementation MPFactor {
diff --git a/MathPad/MPFactorial.h b/MathPad/MPFactorial.h
index 795ae6c..6892404 100644
--- a/MathPad/MPFactorial.h
+++ b/MathPad/MPFactorial.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
 #import "MPValueGroup.h"
 
+@class MPFactorial;
+
 @interface MPFactorial : NSObject <MPValue>
 
 @property (readonly, nonatomic, strong) id<MPValue> value;
diff --git a/MathPad/MPFactorial.m b/MathPad/MPFactorial.m
index c06f1ad..dbae67c 100644
--- a/MathPad/MPFactorial.m
+++ b/MathPad/MPFactorial.m
@@ -8,6 +8,9 @@
 
 #import "MPFactorial.h"
 
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
 @implementation MPFactorial
 
 - (instancetype)init
diff --git a/MathPad/MPFractionFunction.h b/MathPad/MPFractionFunction.h
index bfee7ed..3b9a3ba 100644
--- a/MathPad/MPFractionFunction.h
+++ b/MathPad/MPFractionFunction.h
@@ -6,7 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
+
+@class MPFractionFunction, MPExpression;
 
 @interface MPFractionFunction : MPFunction
 
diff --git a/MathPad/MPFractionFunction.m b/MathPad/MPFractionFunction.m
index 2028e86..73d53e1 100644
--- a/MathPad/MPFractionFunction.m
+++ b/MathPad/MPFractionFunction.m
@@ -8,6 +8,7 @@
 
 #import "MPFractionFunction.h"
 
+#import "MPExpression.h"
 #import "MPExpressionTree.h"
 
 @implementation MPFractionFunction
diff --git a/MathPad/MPFractionFunctionLayout.h b/MathPad/MPFractionFunctionLayout.h
index d35d134..c71597f 100644
--- a/MathPad/MPFractionFunctionLayout.h
+++ b/MathPad/MPFractionFunctionLayout.h
@@ -7,7 +7,8 @@
 //
 
 #import "MPFunctionLayout.h"
-#import "MPFractionFunction.h"
+
+@class MPFractionFunctionLayout, MPFractionFunction;
 
 @interface MPFractionFunctionLayout : MPFunctionLayout
 
diff --git a/MathPad/MPFractionFunctionLayout.m b/MathPad/MPFractionFunctionLayout.m
index 169fa3f..11cafdd 100644
--- a/MathPad/MPFractionFunctionLayout.m
+++ b/MathPad/MPFractionFunctionLayout.m
@@ -7,7 +7,8 @@
 //
 
 #import "MPFractionFunctionLayout.h"
-#import "MPExpressionLayout.h"
+
+#import "MPFractionFunction.h"
 
 #define kFractionFunctionLineWidth 1.0
 #define kFractionFunctionHorizontalInset 2.0
diff --git a/MathPad/MPFunction+MPToken.h b/MathPad/MPFunction+MPToken.h
index 44e45fc..9265abc 100644
--- a/MathPad/MPFunction+MPToken.h
+++ b/MathPad/MPFunction+MPToken.h
@@ -6,7 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
 #import "MPToken.h"
 
 @interface MPFunction (MPToken) <MPToken>
diff --git a/MathPad/MPFunction+MPToken.m b/MathPad/MPFunction+MPToken.m
index eb708f0..27f249a 100644
--- a/MathPad/MPFunction+MPToken.m
+++ b/MathPad/MPFunction+MPToken.m
@@ -8,6 +8,8 @@
 
 #import "MPFunction+MPToken.h"
 
+#import "MPExpression.h"
+
 @implementation MPFunction (MPToken)
 
 - (MPTokenType)tokenType
diff --git a/MathPad/MPFunction+MPValue.h b/MathPad/MPFunction+MPValue.h
index d2e2b07..5e6d9fe 100644
--- a/MathPad/MPFunction+MPValue.h
+++ b/MathPad/MPFunction+MPValue.h
@@ -6,9 +6,8 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
 #import "MPValueGroup.h"
-#import "MPFunction+MPToken.h"
 
 @interface MPFunction (MPValue) <MPValue>
 
diff --git a/MathPad/MPFunction+MPValue.m b/MathPad/MPFunction+MPValue.m
index 09ba9d3..87bf0ab 100644
--- a/MathPad/MPFunction+MPValue.m
+++ b/MathPad/MPFunction+MPValue.m
@@ -8,6 +8,8 @@
 
 #import "MPFunction+MPValue.h"
 
+#import "MPFunction+MPToken.h"
+
 @implementation MPFunction (MPValue)
 
 - (instancetype)initWithTokenStream:(MPTokenStream *)tokenStream
diff --git a/MathPad/MPFunction.h b/MathPad/MPFunction.h
index dd29a18..92d3b94 100644
--- a/MathPad/MPFunction.h
+++ b/MathPad/MPFunction.h
@@ -6,7 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
 #import "MPExpressionElement.h"
 
 #define MPFunctionAccessorImplementation(Accessor, variableName) \
@@ -19,6 +18,7 @@
 }
 
 @class MPFunction, MPExpression, MPRangePath;
+@protocol MPExpressionElement;
 
 @interface MPFunction : NSObject <NSCoding, NSCopying, MPExpressionElement>
 
diff --git a/MathPad/MPFunction.m b/MathPad/MPFunction.m
index 61f4176..b3e37e4 100644
--- a/MathPad/MPFunction.m
+++ b/MathPad/MPFunction.m
@@ -7,18 +7,13 @@
 //
 
 #import "MPFunction.h"
+
 #import "MPExpression.h"
 #import "MPRangePath.h"
-
 #import "NSIndexPath+MPAdditions.h"
 
 @implementation MPFunction
 
-+ (NSString *)localizedFunctionName
-{
-    return NSLocalizedString(@"Function", @"Name of Generic Function.");
-}
-
 #pragma mark Creation Methods
 - (instancetype)init
 {
diff --git a/MathPad/MPFunctionLayout.h b/MathPad/MPFunctionLayout.h
index 5698448..8b2927a 100644
--- a/MathPad/MPFunctionLayout.h
+++ b/MathPad/MPFunctionLayout.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Cocoa;
 #import "MPLayout.h"
 
+@class MPFunctionLayout, MPFunction, MPExpressionLayout;
+
 @interface MPFunctionLayout : MPLayout
 
 + (MPFunctionLayout *)functionLayoutForFunction:(MPFunction *)function
diff --git a/MathPad/MPFunctionLayout.m b/MathPad/MPFunctionLayout.m
index 796dfb0..c27cf4b 100644
--- a/MathPad/MPFunctionLayout.m
+++ b/MathPad/MPFunctionLayout.m
@@ -7,18 +7,21 @@
 //
 
 #import "MPFunctionLayout.h"
-#import "MPFunction.h"
-#import "MPExpressionLayout.h"
 
+#import "MPExpression.h"
+#import "MPFunction.h"
 #import "MPSumFunction.h"
-#import "MPSumFunctionLayout.h"
 #import "MPParenthesisFunction.h"
+#import "MPPowerFunction.h"
+#import "MPFractionFunction.h"
+#import "MPRootFunction.h"
+
+#import "MPExpressionLayout.h"
+#import "MPSumFunctionLayout.h"
 #import "MPParenthesisFunctionLayout.h"
 #import "MPPowerFunctionLayout.h"
 #import "MPFractionFunctionLayout.h"
-#import "MPFractionFunction.h"
 #import "MPRootFunctionLayout.h"
-#import "MPRootFunction.h"
 
 #import "NSIndexPath+MPAdditions.h"
 
diff --git a/MathPad/MPFunctionValue.h b/MathPad/MPFunctionValue.h
index fef3a9a..8728d62 100644
--- a/MathPad/MPFunctionValue.h
+++ b/MathPad/MPFunctionValue.h
@@ -6,11 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
-#import "MPPowerFunction.h"
-#import "MPFunction+MPValue.h"
 #import "MPValueGroup.h"
 
+@class MPFunctionValue, MPPowerFunction, MPValueGroup;
+
 @interface MPFunctionValue : NSObject <MPValue>
 
 @property (readonly, nonatomic, copy) NSString *functionName;
diff --git a/MathPad/MPFunctionValue.m b/MathPad/MPFunctionValue.m
index 5cc58e1..b0853dc 100644
--- a/MathPad/MPFunctionValue.m
+++ b/MathPad/MPFunctionValue.m
@@ -7,6 +7,11 @@
 //
 
 #import "MPFunctionValue.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
 #import "MPMathRules.h"
 
 double defaultFunction(double value) {return value;};
diff --git a/MathPad/MPFunctionsViewController.h b/MathPad/MPFunctionsViewController.h
index a72c1a2..490c785 100644
--- a/MathPad/MPFunctionsViewController.h
+++ b/MathPad/MPFunctionsViewController.h
@@ -6,9 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
-
-@class MPFunctionsCollectionView;
+@class MPFunctionsViewController, MPFunctionsCollectionView;
 
 @interface MPFunctionsViewController : NSViewController
 
diff --git a/MathPad/MPFunctionsViewController.m b/MathPad/MPFunctionsViewController.m
index bd8da4c..0b21c93 100644
--- a/MathPad/MPFunctionsViewController.m
+++ b/MathPad/MPFunctionsViewController.m
@@ -7,16 +7,18 @@
 //
 
 #import "MPFunctionsViewController.h"
-#import "MPFunction.h"
-#import "MPFunctionLayout.h"
 
+#import "MPExpression.h"
+#import "NSString+MPExpressionElement.h"
+#import "MPFunction.h"
 #import "MPSumFunction.h"
 #import "MPParenthesisFunction.h"
 #import "MPPowerFunction.h"
 #import "MPFractionFunction.h"
 
+#import "MPFunctionLayout.h"
 
-@class MPFunctionTemplateItem;
+@class MPFunctionsCollectionView, MPFunctionTemplateView, MPFunctionTemplateItem;
 
 @interface MPFunctionsCollectionView : NSCollectionView
 
diff --git a/MathPad/MPLayout.h b/MathPad/MPLayout.h
index 04486f9..0904be2 100644
--- a/MathPad/MPLayout.h
+++ b/MathPad/MPLayout.h
@@ -6,8 +6,15 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Cocoa;
-#import "MPExpressionStorage.h"
+#define kMPEmptyBoxWidth (self.usesSmallSize ? 2.0 : 3.0)
+#define kMPEmptyBoxHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font))
+#define kMPEmptyBoxYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)))
+
+#define kMPEmptyBoxDrawingWidth kMPEmptyBoxWidth
+#define kMPEmptyBoxDrawingHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font))
+#define kMPEmptyBoxDrawingYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)/2))
+
+@class MPLayout, MPRangePath;
 
 @interface MPLayout : NSObject
 
diff --git a/MathPad/MPLayout.m b/MathPad/MPLayout.m
index 27612f4..59d468a 100644
--- a/MathPad/MPLayout.m
+++ b/MathPad/MPLayout.m
@@ -7,8 +7,8 @@
 //
 
 #import "MPLayout.h"
-#import "MPRangePath.h"
 
+#import "MPRangePath.h"
 #import "NSIndexPath+MPAdditions.h"
 
 @interface MPLayout ()
diff --git a/MathPad/MPMathRules.h b/MathPad/MPMathRules.h
index d14010e..0f9b0b0 100644
--- a/MathPad/MPMathRules.h
+++ b/MathPad/MPMathRules.h
@@ -6,12 +6,12 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-
 FOUNDATION_EXPORT NSString *MPMathRulesMaximumOperatorChainLengthKey;
 FOUNDATION_EXPORT NSString *MPMathRulesMaximumOperatorChainLengthInMultiplicationKey;
 FOUNDATION_EXPORT NSString *MPMathRulesIsUsingDegreesKey;
 
+@class MPMathRules;
+
 @interface MPMathRules : NSObject
 
 + (MPMathRules *)sharedRules;
diff --git a/MathPad/MPNumber.h b/MathPad/MPNumber.h
index d7fbf08..cfb1805 100644
--- a/MathPad/MPNumber.h
+++ b/MathPad/MPNumber.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPValueGroup.h"
 
+@class MPNumber;
+
 @interface MPNumber : NSObject <MPValue>
 
 @property (readonly, nonatomic, strong) NSDecimalNumber *number;
diff --git a/MathPad/MPNumber.m b/MathPad/MPNumber.m
index 53dffdb..d9c787b 100644
--- a/MathPad/MPNumber.m
+++ b/MathPad/MPNumber.m
@@ -8,6 +8,9 @@
 
 #import "MPNumber.h"
 
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
 @implementation MPNumber
 
 - (instancetype)init
diff --git a/MathPad/MPOperatorChain.h b/MathPad/MPOperatorChain.h
index d3ee31d..1e911ca 100644
--- a/MathPad/MPOperatorChain.h
+++ b/MathPad/MPOperatorChain.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
 #import "MPExpressionTreeElement.h"
 
+@class MPOperatorChain;
+
 @interface MPOperatorChain : NSObject <MPExpressionTreeElement>
 
 @property (readonly, nonatomic) BOOL negating;
diff --git a/MathPad/MPOperatorChain.m b/MathPad/MPOperatorChain.m
index 69e89c4..b52209e 100644
--- a/MathPad/MPOperatorChain.m
+++ b/MathPad/MPOperatorChain.m
@@ -8,6 +8,9 @@
 
 #import "MPOperatorChain.h"
 
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
 @implementation MPOperatorChain
 
 - (id)init
diff --git a/MathPad/MPParenthesisFunction.h b/MathPad/MPParenthesisFunction.h
index 31dcfae..0c82fe2 100644
--- a/MathPad/MPParenthesisFunction.h
+++ b/MathPad/MPParenthesisFunction.h
@@ -6,7 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
+
+@class MPParenthesisFunction, MPExpression;
 
 @interface MPParenthesisFunction : MPFunction
 
diff --git a/MathPad/MPParenthesisFunction.m b/MathPad/MPParenthesisFunction.m
index 149883b..4d138ce 100644
--- a/MathPad/MPParenthesisFunction.m
+++ b/MathPad/MPParenthesisFunction.m
@@ -9,6 +9,7 @@
 
 #import "MPParenthesisFunction.h"
 
+#import "MPExpression.h"
 #import "MPExpressionTree.h"
 
 @implementation MPParenthesisFunction
diff --git a/MathPad/MPParenthesisFunctionLayout.h b/MathPad/MPParenthesisFunctionLayout.h
index f5ba164..a1b6037 100644
--- a/MathPad/MPParenthesisFunctionLayout.h
+++ b/MathPad/MPParenthesisFunctionLayout.h
@@ -7,7 +7,8 @@
 //
 
 #import "MPFunctionLayout.h"
-#import "MPParenthesisFunction.h"
+
+@class MPParenthesisFunctionLayout, MPParenthesisFunction;
 
 @interface MPParenthesisFunctionLayout : MPFunctionLayout
 
diff --git a/MathPad/MPParenthesisFunctionLayout.m b/MathPad/MPParenthesisFunctionLayout.m
index 2b324eb..00f83f7 100644
--- a/MathPad/MPParenthesisFunctionLayout.m
+++ b/MathPad/MPParenthesisFunctionLayout.m
@@ -8,6 +8,8 @@
 
 #import "MPParenthesisFunctionLayout.h"
 
+#import "MPParenthesisFunction.h"
+
 #define MPParenthesisFunctionOpeningParensOffset 2
 #define MPParenthesisFunctionClosingParensOffset 0
 
diff --git a/MathPad/MPPowerFunction.h b/MathPad/MPPowerFunction.h
index 0ae7c2f..e69aee3 100644
--- a/MathPad/MPPowerFunction.h
+++ b/MathPad/MPPowerFunction.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
 #import "MPSuffixFunction.h"
 
+@class MPPowerFunction, MPExpression;
+
 @interface MPPowerFunction : MPSuffixFunction
 
 @property (nonatomic, strong) MPExpression *exponentExpression;
diff --git a/MathPad/MPPowerFunction.m b/MathPad/MPPowerFunction.m
index 0b4142c..742049a 100644
--- a/MathPad/MPPowerFunction.m
+++ b/MathPad/MPPowerFunction.m
@@ -7,10 +7,12 @@
 //
 
 #import "MPPowerFunction.h"
-#import "MPExpression.h"
 
+#import "MPExpression.h"
 #import "MPExpressionTree.h"
 
+#import "MPValueGroup.h"
+
 @implementation MPPowerFunction
 
 MPFunctionAccessorImplementation(ExponentExpression, _exponentExpression)
diff --git a/MathPad/MPPowerFunctionLayout.h b/MathPad/MPPowerFunctionLayout.h
index 9aeced3..9d12caa 100644
--- a/MathPad/MPPowerFunctionLayout.h
+++ b/MathPad/MPPowerFunctionLayout.h
@@ -8,7 +8,7 @@
 
 #import "MPFunctionLayout.h"
 
-#import "MPPowerFunction.h"
+@class MPPowerFunctionLayout, MPPowerFunction;
 
 @interface MPPowerFunctionLayout : MPFunctionLayout
 
diff --git a/MathPad/MPPowerFunctionLayout.m b/MathPad/MPPowerFunctionLayout.m
index 506f3cd..ca5ed13 100644
--- a/MathPad/MPPowerFunctionLayout.m
+++ b/MathPad/MPPowerFunctionLayout.m
@@ -7,7 +7,8 @@
 //
 
 #import "MPPowerFunctionLayout.h"
-#import "MPExpressionLayout.h"
+
+#import "MPPowerFunction.h"
 
 #define kPowerFunctionExponentXOffset 1
 #define kPowerFunctionTrailingOffset 2
diff --git a/MathPad/MPProduct.h b/MathPad/MPProduct.h
index b195d61..c43e029 100644
--- a/MathPad/MPProduct.h
+++ b/MathPad/MPProduct.h
@@ -6,9 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPExpressionTreeElement.h"
-#import "MPFactor.h"
+
+@class MPProduct;
 
 @interface MPProduct : NSObject <MPExpressionTreeElement>
 
diff --git a/MathPad/MPProduct.m b/MathPad/MPProduct.m
index 365024b..2d7ffe8 100644
--- a/MathPad/MPProduct.m
+++ b/MathPad/MPProduct.m
@@ -7,8 +7,15 @@
 //
 
 #import "MPProduct.h"
+
+#import "MPFactor.h"
 #import "MPValueGroup.h"
 
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
+
 @implementation MPProduct {
     NSMutableArray *_factors;
 }
diff --git a/MathPad/MPRangePath.h b/MathPad/MPRangePath.h
index 0674a9c..05ee62d 100644
--- a/MathPad/MPRangePath.h
+++ b/MathPad/MPRangePath.h
@@ -6,8 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
-
 #import "MPExpression.h"
 
 #define MPMakeRangePath(loc, len) [MPRangePath rangePathWithLocation:(loc) length:(len)]
diff --git a/MathPad/MPRangePath.m b/MathPad/MPRangePath.m
index c2c46a2..be6eba0 100644
--- a/MathPad/MPRangePath.m
+++ b/MathPad/MPRangePath.m
@@ -7,7 +7,6 @@
 //
 
 #import "MPRangePath.h"
-#import "MPExpression.h"
 
 @implementation MPRangePath
 
diff --git a/MathPad/MPRootFunction.h b/MathPad/MPRootFunction.h
index 30fac2c..f932029 100644
--- a/MathPad/MPRootFunction.h
+++ b/MathPad/MPRootFunction.h
@@ -6,7 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
+
+@class MPRootFunction, MPExpression;
 
 @interface MPRootFunction : MPFunction
 
diff --git a/MathPad/MPRootFunction.m b/MathPad/MPRootFunction.m
index 89924af..3d4db2b 100644
--- a/MathPad/MPRootFunction.m
+++ b/MathPad/MPRootFunction.m
@@ -8,6 +8,7 @@
 
 #import "MPRootFunction.h"
 
+#import "MPExpression.h"
 #import "MPExpressionTree.h"
 
 @implementation MPRootFunction
diff --git a/MathPad/MPRootFunctionLayout.h b/MathPad/MPRootFunctionLayout.h
index 4f95328..5e8fef8 100644
--- a/MathPad/MPRootFunctionLayout.h
+++ b/MathPad/MPRootFunctionLayout.h
@@ -7,7 +7,8 @@
 //
 
 #import "MPFunctionLayout.h"
-#import "MPRootFunction.h"
+
+@class MPRootFunctionLayout, MPRootFunction;
 
 @interface MPRootFunctionLayout : MPFunctionLayout
 
diff --git a/MathPad/MPRootFunctionLayout.m b/MathPad/MPRootFunctionLayout.m
index 0bb20a9..48941fd 100644
--- a/MathPad/MPRootFunctionLayout.m
+++ b/MathPad/MPRootFunctionLayout.m
@@ -8,6 +8,8 @@
 
 #import "MPRootFunctionLayout.h"
 
+#import "MPRootFunction.h"
+
 #define kRootFunctionSpaceBetweenRadicantAndExponent 5
 
 @implementation MPRootFunctionLayout
diff --git a/MathPad/MPSuffixFunction.h b/MathPad/MPSuffixFunction.h
index 2ae51e1..be3d9cc 100644
--- a/MathPad/MPSuffixFunction.h
+++ b/MathPad/MPSuffixFunction.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <MathKit/MathKit.h>
+#import "MPFunction.h"
 
-#import "MPValueGroup.h"
+@class MPSuffixFunction;
+@protocol MPValue;
 
 @interface MPSuffixFunction : MPFunction
 
diff --git a/MathPad/MPSumFunction.h b/MathPad/MPSumFunction.h
index 03a165c..dcbeb0b 100644
--- a/MathPad/MPSumFunction.h
+++ b/MathPad/MPSumFunction.h
@@ -6,7 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
 #import "MPFunction.h"
 
 @class MPSumFunction, MPExpression;
diff --git a/MathPad/MPSumFunction.m b/MathPad/MPSumFunction.m
index b504161..29008f4 100644
--- a/MathPad/MPSumFunction.m
+++ b/MathPad/MPSumFunction.m
@@ -7,11 +7,10 @@
 //
 
 #import "MPSumFunction.h"
+
 #import "MPExpression.h"
-
-#import "MPEvaluationContext.h"
-
 #import "MPExpressionTree.h"
+#import "MPEvaluationContext.h"
 
 @implementation MPSumFunction
 
diff --git a/MathPad/MPSumFunctionLayout.m b/MathPad/MPSumFunctionLayout.m
index c59fee6..b855c7a 100644
--- a/MathPad/MPSumFunctionLayout.m
+++ b/MathPad/MPSumFunctionLayout.m
@@ -7,6 +7,7 @@
 //
 
 #import "MPSumFunctionLayout.h"
+
 #import "MPSumFunction.h"
 
 #import "NSIndexPath+MPAdditions.h"
diff --git a/MathPad/MPSummand.h b/MathPad/MPSummand.h
index 3088aa1..e46fbcb 100644
--- a/MathPad/MPSummand.h
+++ b/MathPad/MPSummand.h
@@ -6,10 +6,9 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPExpressionTreeElement.h"
-#import "MPProduct.h"
-#import "MPOperatorChain.h"
+
+@class MPSummand, MPOperatorChain, MPProduct;
 
 @interface MPSummand : NSObject <MPExpressionTreeElement>
 
diff --git a/MathPad/MPSummand.m b/MathPad/MPSummand.m
index 152972b..eb3126a 100644
--- a/MathPad/MPSummand.m
+++ b/MathPad/MPSummand.m
@@ -7,6 +7,14 @@
 //
 
 #import "MPSummand.h"
+
+#import "MPOperatorChain.h"
+#import "MPProduct.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
 #import "MPMathRules.h"
 
 @implementation MPSummand
diff --git a/MathPad/MPToken.h b/MathPad/MPToken.h
index 58132d8..067d1d7 100644
--- a/MathPad/MPToken.h
+++ b/MathPad/MPToken.h
@@ -6,7 +6,8 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
+@class MPToken;
+@protocol MPToken;
 
 typedef NS_ENUM(NSUInteger, MPTokenType) {
     MPEOFToken = 0,
diff --git a/MathPad/MPTokenStream.h b/MathPad/MPTokenStream.h
index 3a06005..a65965c 100644
--- a/MathPad/MPTokenStream.h
+++ b/MathPad/MPTokenStream.h
@@ -6,8 +6,8 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-#import "MPToken.h"
+@class MPTokenStream;
+@protocol MPToken;
 
 @interface MPTokenStream : NSObject
 
@@ -21,8 +21,8 @@
 
 - (BOOL)hasMoreTokens;
 
-- (MPToken *)currentToken;
-- (MPToken *)peekNextToken;
+- (id<MPToken>)currentToken;
+- (id<MPToken>)peekNextToken;
 - (void)currentTokenConsumed;
 
 @end
diff --git a/MathPad/MPTokenStream.m b/MathPad/MPTokenStream.m
index af71ff0..e7f3249 100644
--- a/MathPad/MPTokenStream.m
+++ b/MathPad/MPTokenStream.m
@@ -8,6 +8,8 @@
 
 #import "MPTokenStream.h"
 
+#import "MPToken.h"
+
 @implementation MPTokenStream {
     NSUInteger _currentTokenIndex;
     NSUInteger eofLocation;
@@ -86,7 +88,7 @@
     return _currentTokenIndex < self.tokens.count;
 }
 
-- (MPToken *)currentToken
+- (id<MPToken>)currentToken
 {
     [self skipWhitespaces];
     if (_currentTokenIndex >= _tokens.count) {
@@ -95,11 +97,11 @@
     return _tokens[_currentTokenIndex];
 }
 
-- (MPToken *)peekNextToken
+- (id<MPToken>)peekNextToken
 {
     NSUInteger currentTokenIndex = _currentTokenIndex;
     [self currentTokenConsumed]; // Pretend the current token has been consumed
-    MPToken *token = [self currentToken];
+    id<MPToken> token = [self currentToken];
     _currentTokenIndex = currentTokenIndex; // Undo the lookahead
     return token;
 }
diff --git a/MathPad/MPUnexpectedSymbolValue.h b/MathPad/MPUnexpectedSymbolValue.h
index ee54543..708178e 100644
--- a/MathPad/MPUnexpectedSymbolValue.h
+++ b/MathPad/MPUnexpectedSymbolValue.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
 #import "MPValueGroup.h"
 
+@class MPUnexpectedSymbolValue;
+
 @interface MPUnexpectedSymbolValue : NSObject <MPValue>
 
 @property (readonly, nonatomic, copy) NSString *symbol;
diff --git a/MathPad/MPUnexpectedSymbolValue.m b/MathPad/MPUnexpectedSymbolValue.m
index ccd8dd3..87ae1ce 100644
--- a/MathPad/MPUnexpectedSymbolValue.m
+++ b/MathPad/MPUnexpectedSymbolValue.m
@@ -8,6 +8,11 @@
 
 #import "MPUnexpectedSymbolValue.h"
 
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
+
 @implementation MPUnexpectedSymbolValue
 
 - (instancetype)init
diff --git a/MathPad/MPValueGroup.h b/MathPad/MPValueGroup.h
index 840bc33..2dcabfb 100644
--- a/MathPad/MPValueGroup.h
+++ b/MathPad/MPValueGroup.h
@@ -6,8 +6,11 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPExpressionTreeElement.h"
+#import "MPTokenStream.h"
+
+@class MPValueGroup;
+@protocol MPValue;
 
 @protocol MPValue <MPExpressionTreeElement>
 
diff --git a/MathPad/MPValueGroup.m b/MathPad/MPValueGroup.m
index d3fc944..40b2379 100644
--- a/MathPad/MPValueGroup.m
+++ b/MathPad/MPValueGroup.m
@@ -7,12 +7,17 @@
 //
 
 #import "MPValueGroup.h"
+
 #import "MPNumber.h"
 #import "MPVariable.h"
-#import "MPFunction+MPValue.h"
-#import "MPUnexpectedSymbolValue.h"
 #import "MPFunctionValue.h"
+#import "MPUnexpectedSymbolValue.h"
 #import "MPFactorial.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
 #import "MPSuffixFunction.h"
 
 @implementation MPValueGroup {
diff --git a/MathPad/MPVariable.h b/MathPad/MPVariable.h
index 8d0bba4..bb801d3 100644
--- a/MathPad/MPVariable.h
+++ b/MathPad/MPVariable.h
@@ -6,9 +6,10 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
 #import "MPValueGroup.h"
 
+@class MPVariable;
+
 @interface MPVariable : NSObject <MPValue>
 
 @property (readonly, nonatomic, strong) NSString *variableName;
diff --git a/MathPad/MPVariable.m b/MathPad/MPVariable.m
index eb7ebfd..594002d 100644
--- a/MathPad/MPVariable.m
+++ b/MathPad/MPVariable.m
@@ -7,6 +7,11 @@
 //
 
 #import "MPVariable.h"
+
+#import "MPTokenStream.h"
+#import "MPToken.h"
+
+#import "MPExpression.h"
 #import "MPEvaluationContext.h"
 
 @implementation MPVariable {
diff --git a/MathPad/MPWhiteView.h b/MathPad/MPWhiteView.h
index 01c3d4a..a0b5457 100644
--- a/MathPad/MPWhiteView.h
+++ b/MathPad/MPWhiteView.h
@@ -6,7 +6,7 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Cocoa/Cocoa.h>
+@class MPWhiteView;
 
 @interface MPWhiteView : NSView
 
diff --git a/MathPad/NSIndexPath+MPAdditions.h b/MathPad/NSIndexPath+MPAdditions.h
index f40ab5d..1e0e21c 100644
--- a/MathPad/NSIndexPath+MPAdditions.h
+++ b/MathPad/NSIndexPath+MPAdditions.h
@@ -6,8 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
-
 @interface NSIndexPath (MPAdditions)
 
 - (NSUInteger)firstIndex;
diff --git a/MathPad/NSRegularExpression+MPParsingAdditions.h b/MathPad/NSRegularExpression+MPParsingAdditions.h
index 58f4c18..bb98bb3 100644
--- a/MathPad/NSRegularExpression+MPParsingAdditions.h
+++ b/MathPad/NSRegularExpression+MPParsingAdditions.h
@@ -6,8 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-
 #define MPStringRange(string) NSMakeRange(0, [string length])
 #define MPStringRangeFrom(from, string) NSMakeRange(from, [string length]-from)
 
diff --git a/MathPad/NSString+MPExpressionElement.h b/MathPad/NSString+MPExpressionElement.h
index 59a0cdf..96d138b 100644
--- a/MathPad/NSString+MPExpressionElement.h
+++ b/MathPad/NSString+MPExpressionElement.h
@@ -6,7 +6,6 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
-@import Foundation;
 #import "MPExpressionElement.h"
 
 @interface NSString (MPExpressionElement) <MPExpressionElement>