reserve a,b,c for boolean object;
reserve p,q,r,s,A,B,C for Element of LTLB_WFF,
        F,G,X,Y for Subset of LTLB_WFF,
        i,j,k,n for Element of NAT,
        f,f1,f2,g for FinSequence of LTLB_WFF;
reserve M for LTLModel;

theorem Th16:
  (SAT M).[n,('X'('not' B))=>('not'('X' B))]=1
 proof
  A1: (SAT M).[n,('not'('X' B))]=0 or(SAT M).[n,('not'('X' B))]=1 by
XBOOLEAN:def 3;
  thus(SAT M).[n,('X'('not' B))=>('not'('X' B))]=(SAT M).[n,('X'('not' B))]=>(
SAT M).[n,('not'('X' B))] by Def11
   .=1 by A1,Th14;
 end;
