reserve A,B,p,q,r,s for Element of LTLB_WFF,
  n for Element of NAT,
  X for Subset of LTLB_WFF,
  g for Function of LTLB_WFF,BOOLEAN,
  x,y for set;
reserve P,Q,P1,R for PNPair;

theorem Th27: [<*>LTLB_WFF,<*>LTLB_WFF]^ = TVERUM '&&' TVERUM
  proof
    len <*>l = 0;
    then len nega <*>l = 0 by LTLAXIO2:def 4;
    then nega <*>l = 0;
    hence [<*>l,<*>l]^ = TVERUM '&&' TVERUM by LTLAXIO2:10;
  end;
