What is the difference with properties declared in header and implementation file
<p>i really think Paul's lectures are great.. i just have a question maybe someone could answer if they don't mind.. In lecture 4, when implementing the new api to the CalculatorBrain class, why was the (id)program property declared in the header file (making it a public property), why not declared in the implementation file like the programStack property. Also, are the accessor methods of properties declared in the implementation files (essentially private properties like the programStack) publicly available? I see he calls the self.program 
stack in the instance method "performOperation"). Would really appreciate it if someone would assist. :)</p>
