gistfile1.txt

// In the header
@interface MyClass : NSObject

@property (readwrite, assign) int a;

@end

// In a separate header that you include in all MyClass subclasses
@interface MyClass (Protected)

@property (readwrite, assign) int b;

@end

// In MyClass.m
@interface MyClass ()

@property (readwrite, assign) int c;

@end

@implementation MyClass

@synthesize ...

@end