theorem Th44:
  for G being UnContinuous TopGroup holds inverse_op G is Homeomorphism of G
proof
  let G be UnContinuous TopGroup;
  set f = inverse_op G;
  thus
 dom f = [#]G & rng f = [#]G & f is one-to-one by FUNCT_2:def 1,def 3;
  thus f is continuous by Def7;
  f = (f qua Function)" by Th13
    .= f/" by TOPS_2:def 4;
  hence thesis by Def7;
end;
