Internal Redesign:

- Combined MPExpression and MPMutableExpression
- Abstracted children of MPExpression into MPExpressionElement protocol
- Abstracted most of MPExpressionLayout and MPFunctionLayout into common superclass MPLayout

MathPad/MPRangePath.h

@@ -6,8 +6,12 @@
 //  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
 //
 
+@import Foundation;
+
 #import "MPExpression.h"
 
+@class MPRangePath, MPExpression;
+
 @interface MPRangePath : NSObject <NSCopying, NSCoding>
 
 #pragma mark Creation Methods