reserve a,b,p,x,x9,x1,x19,x2,y,y9,y1,y19,y2,z,z9,z1,z2 for object,
   X,X9,Y,Y9,Z,Z9 for set;
reserve A,D,D9 for non empty set;
reserve f,g,h for Function;

theorem
  f c= g implies Y|`f|X c= Y|`g|X
proof
  assume f c= g;
  then Y|`f c= Y|`g by RELAT_1:101;
  hence thesis by RELAT_1:76;
end;
