CHECK_ASSUME_TAC : thm_tactic
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} ?- tUnless A' is a subset of A, the tactic will be invalid, although it will not fail.