reserve n for Nat;

theorem prl3:
for R being Ring, a being Element of R holds 2 '*' a = a + a
proof
let R be Ring, a be Element of R;
thus 2 '*' a = (1 + 1) '*' a
            .= 1 '*' a + 1 '*' a by RING_3:62
            .= a + 1 '*' a by RING_3:60
            .= a + a by RING_3:60;
end;
