Give a formal definition of the term extended stack in

Question

Problem

1. Give a formal definition of the term extended stack.

2. In mathematics the Cartesian product of sets T₁, T₂,... ,T_n is defined as the set of all n-tuples (t₁, t₂,... ,t_n), where ti is a member of Ti for all i, 1 ≤ i ≤ n. Use the Cartesian product to give a precise definition of a class.