proposition: Lemma combine_sext: forall sz1 (w1: word sz1) sz2 (w2: word (S sz2)) n, existT word _ (combine w1 (sext w2 n)) = existT word _ (sext (combine w1 w2) n).
proof: Proof. unfold sext; intros. rewrite wmsb_combine with (b2:= false) by discriminate. destruct (wmsb w2 false); apply combine_assoc_existT. Qed.
imports: Coq.Classes.Morphisms Coq.Classes.Morphisms_Prop Coq.Classes.Equivalence Coq.Arith.PeanoNat Coq.ZArith.BinInt  Coq.Arith.Arith Coq.NArith.NArith Coq.Bool.Bool Coq.ZArith.ZArith Coq.Logic.Eqdep_dec Coq.Logic.EqdepFacts Coq.Program.Tactics Coq.Program.Equality Coq.setoid_ring.Ring Coq.setoid_ring.Ring_polynom bbv.Nomega bbv.ZLib bbv.NatLib bbv.NLib bbv.N_Z_nat_conversions bbv.DepEq bbv.DepEqNat bbv.ReservedNotations Coq.micromega.Lia