theorem Th23:
  L is D_Lattice implies the L_meet of L is_distributive_wrt the L_join of L
proof
  assume
A1: L is D_Lattice;
  now
    let a,b,c;
    thus (the L_meet of L).(a,(the L_join of L).(b,c)) = a "/\" (b "\/" c)
      .= (a "/\" b) "\/" (a "/\" c) by A1,LATTICES:def 11
      .= (the L_join of L).((the L_meet of L).(a,b),(the L_meet of L).(a,c));
  end;
  hence thesis by BINOP_1:12;
end;
