theorem Th14:
  (0.X) .|. x = 0
proof
  09(X) .|. x = (x + (-x)) .|. x by RLVECT_1:5
    .= x .|. x + (-x) .|. x by Def2
    .= x .|. x + ( - x .|. x ) by Th8;
  hence thesis;
end;
