Record equiv_rel := EquivRelPack {
  equiv :> rel T;
  _ : equiv_class_of equiv
}.Record equiv_rel := EquivRelPack {
  equiv :> rel T;
  _ : equiv_class_of equiv
}.Record equiv_rel := EquivRelPack {
  equiv :> rel T;
  _ : equiv_class_of equiv
}.Definition equiv_pack (r : rel T) ce of phant_id ce equiv_class :=
  @EquivRelPack r ce.

Lemma equiv_sym : symmetric e.