reserve
  X,x,y,z for set,
  k,n,m for Nat ,
  f for Function,
  p,q,r for FinSequence of NAT;
reserve p1,p2,p3 for FinSequence;
reserve T,T1 for Tree;
reserve fT,fT1 for finite Tree;
reserve t for Element of T;
reserve w for FinSequence;

theorem Th35:
  { w } is AntiChain_of_Prefixes-like
proof
  thus for x st x in { w } holds x is FinSequence by TARSKI:def 1;
  let p1,p2;
  assume that
A1: p1 in { w } and
A2: p2 in { w };
 p1 = w by A1,TARSKI:def 1;
  hence thesis by A2,TARSKI:def 1;
end;
