reserve L for Ortholattice,
  a, b, c for Element of L;

theorem
  a _|_ a iff a = Bottom L
proof
  thus a _|_ a implies a = Bottom L
  proof
    assume a_|_a;
    then a [= a`;
    then a "/\" a` = a by LATTICES:4;
    hence thesis by Th2;
  end;
  assume a = Bottom L;
  then a "/\" a` = a;
  then a [= a` by LATTICES:4;
  hence thesis;
end;
