ACL2-PC_colon__colon_IN-THEORY.html -- ACL2 Version 6.3

### ACL2-PC::IN-THEORY

(primitive) `` set the current proof-checker theory

    Major Section:  PROOF-CHECKER-COMMANDS

    Example:
    (in-theory
       (union-theories (theory 'minimal-theory) '(true-listp binary-append)))

    General Form:
    (in-theory &optional atom-or-theory-expression)

If the argument is not supplied, then this command sets the current proof-checker theory (see below for explanation) to agree with the current ACL2 theory. Otherwise, the argument should be a theory expression, and in that case the proof-checker theory is set to the value of that theory expression.

The current proof-checker theory is used in all calls to the ACL2 theorem prover and rewriter from inside the proof-checker. Thus, the most recent `in-theory` instruction in the current `state-stack` has an effect in the proof-checker totally analogous to the effect caused by an `in-theory` hint or event in ACL2. All `in-theory` instructions before the last are ignored, because they refer to the current theory in the ACL2 `state`, not to the existing proof-checker theory. For example:

       ACL2 !>:trans1 (enable bar)
        (UNION-THEORIES (CURRENT-THEORY :HERE)
                        '(BAR))
       ACL2 !>:trans1 (CURRENT-THEORY :HERE)
        (CURRENT-THEORY-FN :HERE WORLD)
       ACL2 !>

Thus `(in-theory (enable bar))` modifies the current theory of the current ACL2 world. So for example, suppose that `foo` is disabled outside the proof checker and you execute the following instructions, in this order.

       (in-theory (enable foo))
       (in-theory (enable bar))

Then after the second of these, `bar` will be enabled in the proof-checker, but `foo` will be disabled. The reason is that `(in-theory (enable bar))` instructs the proof-checker to modify the current theory (from outside the proof-checker, not from inside the proof-checker) by enabling `bar`.

Note that `in-theory` instructions in the proof-checker have no effect outside the proof-checker's interactive loop.

If the most recent `in-theory` instruction in the current state of the proof-checker has no arguments, or if there is no `in-theory` instruction in the current state of the proof-checker, then the proof-checker will use the current ACL2 theory. This is true even if the user has interrupted the interactive loop by exiting and changing the global ACL2 theory. However, if the most recent `in-theory` instruction in the current state of the proof-checker had an argument, then global changes to the current theory will have no effect on the proof-checker state.