proposition: Lemma minus_eqv_rel_helper A (R T: relation A) d1 d2: ⦗d1⦘ ⨾ (R \ T) ⨾ ⦗d2⦘ ≡ (⦗d1⦘ ⨾ R ⨾ ⦗d2⦘) \ T.
proof: Proof. red; split; unfold inclusion, eqv_rel, minus_rel, seq; ins; desf; firstorder. Qed.
imports: Program.Basics Arith micromega.Lia Permutation List Setoid HahnBase HahnList HahnRelationsBasic HahnSets