Tactic.CHECK_ASSUME

When applied to a theorem A' |- s and a goal A ?- t, the tactic CHECK_ASSUME_TAC checks whether the theorem will solve the goal (this includes the possibility that the theorem is just A' |- F). If so, the goal is duly solved. If not, the theorem is added to the assumptions of the goal, unless it is already there.

       A ?- t
   ==============  CHECK_ASSUME_TAC (A' |- F)   [special case 1]


       A ?- t
   ==============  CHECK_ASSUME_TAC (A' |- t)   [special case 2]


       A ?- t
   ==============  CHECK_ASSUME_TAC (A' |- s)   [general case]
    A u {s} ?- t

Unless A' is a subset of A, the tactic will be invalid, although it will not fail.