theorem
  for G being Abelian left-distributive doubleLoop holds (-1.G)*(-1.G) = 1.G
proof
  let G be Abelian left-distributive doubleLoop;
  thus (-1.G)*(-1.G) = -(1_G*(-1.G)) by Th7
    .= -(-1.G)
    .= 1.G by Th3;
end;
