
theorem t2:
for R being 2-characteristic Ring, a being Element of R holds -a = a
proof
let R be 2-characteristic Ring, a be Element of R;
Char R = 2 by RING_3:def 6; then
0.R * a = (2 '*' 1.R) * a by RING_3:def 5
       .= 2 '*' (1.R * a) by REALALG2:5 .= a + a by RING_5:2;
hence thesis by RLVECT_1:6;
end;
