Consider the following classes:

Expression represents algebraic expressions, including prefix, postfix, and infix expressions. Its public methods include character At. Its protected methods include is Operator and is identifier. It also has several private methods.

Infix Expression is derived from Expression and represents infix expressions. Its public methods include is Legal and evaluate. It also has several protected and private methods.

a What methods can the implementation of is identifier invoke?

b. What methods can the implementation of isle gal invoke?