Add a Set card class to the model
Add properties that represent a set card
Add public class methods that return the valid values for the properties of a set card
Implement maxSymbols class method
Implement validSymbols class method
Implement the validColors class method
Implement validShading class method
Create setter for nrSymbols property
Add an enumerator that specifies the size of the enumeration
Add a setter for the color property
Add setter for the shading property
Add getter for the symbol property (with lazy instantiation)
Add setter for the symbol property
Overwrite the contents property getter, for use with a SetCard
Overwrite the match method to be useful for a set game card
Create the comparison method stubs
Add the current card to an array that is passed to the comparison methods in the match method
Create method to verify that the array passed to the comparison methods, is of 3 set game cards
Implement the compareSymbols method

If the symbols of the 3 cards don’t all match then return NO.
Implement the compareShading method

If the 3 cards don’t have the same shading return NO.