SET-DIFFERENCE-THEORIES.html -- ACL2 Version 6.3

## SET-DIFFERENCE-THEORIES

difference of two theories

    Major Section:  THEORIES

    Example:
    (set-difference-theories (current-theory :here)
                             '(fact (fact)))

    General Form:
    (set-difference-theories th1 th2)

where `th1` and `th2` are theories (see theories). To each of the arguments there corresponds a runic theory. This function returns the set-difference of those two runic theories, represented as a list and ordered chronologically. That is, a rune is in the result iff it is in the first runic theory but not in the second.

The standard way to ``disable'' a theory, `lst`, is: `(in-theory (set-difference-theories (current-theory :here) lst))`.

This ``function'' is actually a macro that expands to a term mentioning the single free variable `world`. When theory expressions are evaluated by `in-theory` or the `:``in-theory` hint, `world` is bound to the current ACL2 world.