proposition: Lemma ZToWord_minus: forall sz a b, ZToWord sz (a - b) = ZToWord sz a ^- ZToWord sz b.
proof: Proof. intros. rewrite wminus_wminusZ. unfold wminusZ, wordBinZ. destruct (wordToZ_ZToWord' sz a) as [k1 D1]. rewrite D1. clear D1. destruct (wordToZ_ZToWord' sz b) as [k2 D2]. rewrite D2. clear D2. rewrite wminusZ_helper. symmetry. apply ZToWord_Npow2_sub_z. 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