reserve x for object, X,Y for set;
reserve C for non empty set;
reserve c for Element of C;
reserve f,f1,f2,f3,g,g1 for complex-valued Function;
reserve r,p for Complex;

theorem
  f3(#)f1 - f3(#)f2 = f3(#)(f1 - f2) by Th14;
