fact: Fixpoint append_word (s: formula) (v: list bool) := match v with | [] => s | a :: v => if a then append_word (arr b2 s) v else append_word (arr b3 s) v end.
imports: List Lia ssreflect ssrbool ssrfun Undecidability.HilbertCalculi.HSC Undecidability.HilbertCalculi.Util.HSCFacts Undecidability.PCP.PCP