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
  Y|`R = R*(id Y)
proof
  let x,y;
  [x,y] in Y|`R iff y in Y & [x,y] in R by Def10;
  hence thesis by Th43;
end;
