theorem
  for G being strict trivial Group, H being strict Group holds
  G,H are_isomorphic implies H is trivial
proof
  let G be strict trivial Group, H be strict Group;
  assume
A1: G,H are_isomorphic;
  then reconsider H as finite Group by Th74;
  card G = 1 by Th11;
  then card H = 1 by A1,Th73;
  hence thesis by Th11;
end;
