attach code for execution
Major Section:  ACL2-BUILT-INS

The form (must-be-equal logic exec) evaluates to logic in the ACL2 logic but evaluates to exec in raw Lisp. The point is to be able to write one definition to reason about logically but another for evaluation. Please see mbe and see mbt for appropriate macros to use, rather than calling must-be-equal directly, since it is easy to commute the arguments of must-be-equal by accident.

In essence, the guard for (must-be-equal x y) is (equal x y). However, note that must-be-equal is a macro: (must-be-equal logic exec) expands to (mbe1 exec logic), which expands to a call of return-last.