reserve L for D_Lattice;
reserve a, b, c for Element of L;
reserve L for B_Lattice;
reserve a, b for Element of L;

theorem
  a [= b implies b` [= a`
proof
  assume a [= b;
  then b`"/\"a [= b`"/\"b by Th7;
  then
A1: b`"/\"a [= Bottom L by Th18;
  Bottom L [= b`"/\"a;
  then b `"/\"a = Bottom L by A1,Th6;
  hence thesis by Th23;
end;
