proposition: Lemma nfaP x : reflect (exists s r, s \in nfa_s M /\ nfa_run x s r) (x \in nfa_lang M).
proof: Proof. apply: (iffP exists_inP). - case => s ? /nfa_acceptP [r] ?. by exists s; exists r. - case => s [r] [? ?]. exists s => //. apply/nfa_acceptP. by exists r. Qed.
imports: mathcomp(all_ssreflect) RegLang(misc languages dfa)