PURE_REWRITE_RULE : (thm list -> thm -> thm)
Rewrites a theorem with only the given list of rewrites.
This rule provides a method for rewriting a theorem with the theorems given,
and excluding simplification with tautologies in implicit_rewrites. Matching
subterms are found recursively starting from the term in the conclusion part of
the theorem, until no more matches are found. For more details on rewriting see
PURE_REWRITE_RULE is useful when the simplifications that arise by
rewriting a theorem with implicit_rewrites are not wanted.
Does not fail. May result in divergence, in which case
PURE_ONCE_REWRITE_RULE can be used.