reserve I,X,x,d,i for set;
reserve M for ManySortedSet of I;
reserve EqR1,EqR2 for Equivalence_Relation of X;

theorem Th1:
  EqR1 "\/" EqR2 = EqCl (EqR1 \/ EqR2)
proof
A1: for EqR3 be Equivalence_Relation of X st EqR1 \/ EqR2 c= EqR3 holds EqR1
  "\/" EqR2 c= EqR3 by EQREL_1:def 2;
  EqR1 \/ EqR2 c= EqR1 "\/" EqR2 by EQREL_1:def 2;
  hence thesis by A1,Def1;
end;
