theorem Th14:
  (for v holds u "\/" v = v) implies u = Bottom L
proof
  assume
A1: u "\/" v = v;
  now
    let v;
    v "\/" u = v by A1;
    then u [= v;
    hence v "/\" u = u by LATTICES:4;
  end;
  hence thesis by RLSUB_2:64;
end;
