reserve A,X,X1,X2,Y,Y1,Y2 for set, a,b,c,d,x,y,z for object;
reserve P,P1,P2,Q,R,S for Relation;

theorem Th94:
  X c= Y implies X|`R c= Y|`R
proof
  assume
A1: X c= Y;
  let x,y;  [x,y] in X|`R iff [x,y] in R & y in X by Def10;
  hence thesis by A1,Def10;
end;
