theorem th265:
  F |= A & (for B st B in F holds {}LTLB_WFF |=0 B)
    implies {}LTLB_WFF |=0 A
proof
  assume
Z1: F |= A & (for B st B in F holds {}LTLB_WFF |=0 B);then
  for B st B in F holds {}LTLB_WFF |= B by th262b,th264p;
  hence {}LTLB_WFF |=0 A by th262b,th264p,th218,Z1;
end;
