theorem Th49:
  for f,g being Function st dom f = X & dom g = X & x in X holds
  <:f,g:>.x = [f.x,g.x]
proof
  let f,g be Function;
  assume dom f = X & dom g = X & x in X;
  then x in dom f /\ dom g;
  then x in dom <:f,g:> by Def7;
  hence thesis by Def7;
end;
