
theorem c10a:
for R being preordered Ring,
    P being Preordering of R,
    a,b being Element of R holds a <=P, b iff (-b) <=P, (-a)
proof
let R be preordered Ring, P be Preordering of R, a,b be Element of R;
(-a) - (-b) = -a + b;
hence thesis;
end;
