theorem Th42:
  for G being BinContinuous TopaddGroup, a being Element of G holds
a+ is Homeomorphism of G
proof
  let G be BinContinuous TopaddGroup, a be Element of G;
  set f = a+;
  thus dom f = [#]G & rng f = [#]G & f is one-to-one by FUNCT_2:def 1,def 3;
  thus f is continuous;
  f/" = ((-a)+) by Th17;
  hence thesis;
end;
