reserve i,j,k,n,m for Nat,
  x,y,z,y1,y2 for object, X,Y,D for set,
  p,q for XFinSequence;

theorem Th6:
  n >= len p implies p/^n={}
proof
  assume n>=len p;
  then len p-'n=0 by NAT_2:8;
  then len (p/^n)=0 by Def2;
  hence thesis;
end;
