proposition: Lemma sext_eq_rect: forall sz (w: word sz) n nsz Hsz1, exists Hsz2, eq_rect (sz + n) word (sext w n) (nsz + n) Hsz1 = sext (eq_rect sz word w nsz Hsz2) n.
proof: Proof. intros. assert (Hsz: sz = nsz) by lia. exists Hsz. subst; simpl. eq_rect_simpl. reflexivity. 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