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 Th22:
  X [= Y implies Z \ Y [= Z \ X
proof
  assume X [= Y;
  then Y` [= X` by LATTICES:26;
  hence thesis by LATTICES:9;
end;
