fact: Definition mk_iff (k: kind) (pol:bool) (f1 f2: TFormula TX AF k):= or_cnf_opt (and_cnf_opt (REC (negb pol) f1) (REC false f2)) (and_cnf_opt (REC pol f1) (REC true f2)).
imports: List Refl Bool Relation_Definitions Setoid