reserve A,B,C,D,p,q,r for Element of LTLB_WFF,
        F,G,X for Subset of LTLB_WFF,
        M for LTLModel,
        i,j,n for Element of NAT,
        f,f1,f2,g for FinSequence of LTLB_WFF;

theorem th263pb:
  M |=0 A iff M |=0 {A}
  proof
    thus M |=0 A implies M |=0 {A} by TARSKI:def 1;
    A in {A} by TARSKI:def 1;
    hence thesis;
  end;
