RESQ_REWRITE1_TAC takes an equational theorem which is restricted universally
quantified at the outer level. It calls RESQ_REWR_CANON to convert
the theorem to the form accepted by COND_REWR_TAC and passes the
resulting theorem to this tactic which carries out conditional
rewriting.
Suppose that th is the following theorem
Applying the tactic RESQ_REWRITE1_TAC th to a goal (asml,gl)
will return a main subgoal (asml',gl') where gl' is obtained by
substituting instances of R[x'/x] for corresponding instances of
Q[x'/x] in the original goal gl. All instances of P x' which
do not appear in the original assumption asml are added to it to
form asml', and they also become new subgoals (asml,P x').