Given a theorem-tactic ttac and a theorem A |- t, the function
ANTE_RES_THEN produces a tactic that attempts to match t to the antecedent
of each implication
   Ai |- !x1...xn. ui ==> vi
   ANTE_RES_THEN ttac (A |- t) g
   MAP_EVERY ttac [A1 u A |- v1, ..., Am u A |- vm] g