reserve x, y for object, X, X1, X2 for set;
reserve Y, Y1, Y2 for complex-functions-membered set,
  c, c1, c2 for Complex,
  f for PartFunc of X,Y,
  f1 for PartFunc of X1,Y1,
  f2 for PartFunc of X2, Y2,
  g, h, k for complex-valued Function;

theorem Th62:
  x in dom(f<->g) implies (f<->g).x = f.x - g.x
proof
  assume x in dom(f<->g);
  hence (f<->g).x = f.x + (-g).x by Def41
    .= f.x - g.x by VALUED_1:8;
end;
