Rewrites a term once with only the given list of rewrites.
DESCRIPTION
PURE_ONCE_REWRITE_CONV generates rewrites from the list of theorems
supplied by the user, without including the tautologies given in
basic_rewrites. The applicable rewrites are employed once, without
entailing in a recursive search for matches over the term.
See GEN_REWRITE_CONV for more details about rewriting strategies in
HOL.