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` [= (X "/\" Y)`
proof
  X` [= X` "\/" Y` by LATTICES:5;
  hence thesis by LATTICES:23;
end;
