let V be non empty right_complementable add-associative right_zeroed addLoopStr ; :: thesis: for v, w being Element of V st v - w = 0. V holds
v = w
let v, w be Element of V; :: thesis: ( v - w = 0. V implies v = w )
assume v - w = 0. V ; :: thesis: v = w
then - v = - w by Def10;
hence v = w by Th18; :: thesis: verum