
theorem Th4:
  for I being set
  for F being associative Group-like multMagma-Family of I
  holds F is Group-yielding
proof
  let I be set;
  let F be associative Group-like multMagma-Family of I;
  let y be object;
  assume y in rng F;
  then ex x being object st x in dom F & y = F.x by FUNCT_1:def 3;
  hence y is Group by GROUP_19:1;
end;
