proposition: Lemma restr_union A (f : A -> Prop) r r' : restr_rel f (r ∪ r') ≡ restr_rel f r ∪ restr_rel f r'.
proof: Proof. u. Qed.
imports: Program.Basics Arith micromega.Lia Permutation List Setoid HahnBase HahnList HahnRelationsBasic HahnSets