theorem Th70:
  latt (L,P) = (latt (L.:,P.:)).:
proof
  (ex o1, o2 st o1 = join(L)||P & o2 = met(L)||P & latt (L,P) = LattStr
  (#P, o1, o2#) )& ex o3, o4 being BinOp of P.: st o3 = join(L.:)||(P.:) & o4 =
  met (L.:)||(P.:) & latt (L.:,P.:) = LattStr (#P.:, o3, o4#) by Def14;
  hence thesis;
end;
