Some small corrections

Added example expression (hardcoded for development)
Added example change for expressions (hardcoded for development)

MathPad/MPExpressionView.m

@@ -14,9 +14,6 @@
 
 #import "MPSumFunction.h"
 
-@interface MPExpressionView ()
-@end
-
 @implementation MPExpressionView
 
 #pragma mark Creation Methods
@@ -50,12 +47,20 @@
 
 - (void)initializeObjects
 {
-    MPExpressionStorage *expressionStorage = [[MPExpressionStorage alloc] initWithSymbols:@[@"12345", [[MPSumFunction alloc] init]]];
+    MPExpressionStorage *expressionStorage = [[MPExpressionStorage alloc] initWithSymbols:@[@"12 345", [[MPSumFunction alloc] init], [[MPSumFunction alloc] init]]];
     _expressionStorage = expressionStorage;
+    [self.expressionLayout setExpressionView:self];
 }
 
 #pragma mark Properties
 
+- (void)setExpressionStorage:(MPExpressionStorage *)expressionStorage
+{
+    [_expressionStorage.expressionLayout setExpressionView:nil];
+    _expressionStorage = expressionStorage;
+    [_expressionStorage.expressionLayout setExpressionView:self];
+}
+
 - (MPExpressionLayout *)expressionLayout
 {
     return self.expressionStorage.expressionLayout;