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 & Z [= V implies X \ V [= Y \ Z
proof
  assume X [= Y & Z [= V;
  then X \ V [= Y \ V & Y \ V [= Y \ Z by Th22,LATTICES:9;
  hence thesis by LATTICES:7;
end;
