Write the functions initialize, push, top, pop, and liststack to maintain a global stack. These functions should behave: > (initialize) nil > (push ‘foo) foo > (push ‘bar) bar > (top) bar >...

Write the functions initialize, push, top, pop, and liststack to maintain a global stack. These functions should behave:

> (initialize) nil

> (push ‘foo)

foo

> (push ‘bar)

bar

> (top)

bar

> (list-stack)

(bar foo)

> (pop)

bar

> (list-stack)

(foo)

> (pop)

foo

> (list-stack)

()