reserve L for Lattice;
reserve X,Y,Z,V for Element of L;
reserve L for D_Lattice;
reserve X,Y,Z for Element of L;
reserve L for 0_Lattice;
reserve X,Y,Z for Element of L;
reserve L for B_Lattice;
reserve X,Y,Z,V for Element of L;

theorem
  (X \ Y)` = X` "\/" Y
proof
  (X \ Y)` = X` "\/" Y`` by LATTICES:23;
  hence thesis;
end;
