Functions for Manipulating these Objects

Consider a typical ``stack'' of control frames.

Suppose the model required that we express the idea of ``the most recent
frame whose return program counter points into

The natural expression of this notion involves

**function application** — ``fetch the

**case analysis** — ``**if** the pc is **then**
...''

**iteration** or **recursion** — ``pop this frame off and
repeat.''

The designers of ACL2 have taken the position that a **programming**
**language** is the natural language in which to define such notions,
**provided** the language has a mathematical foundation so that models can
be analyzed and properties derived logically.

Common Lisp is the language supported by ACL2. To be precise, a small applicative subset of Common Lisp is the language supported by ACL2.