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 Th72:
  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 Def43
    .= f.x (/) g.x by VALUED_1:10;
end;
