-- removed "check_is_fol" from "make_nnf" so that the NNF procedure doesn't check whether a thm is FOL. -- added "check_is_fol_term", which is the same as "check_is_fol", but takes a "term" as input. -- added "check_is_fol" and "check_is_fol_term" into the signature.

tuned document;

tuned;