reserve D for non empty set;
reserve s for FinSequence of D;
reserve m,n for Element of NAT;

theorem Th2:
  for m,n,l be non zero Element of NAT,
  s be Element of n-tuples_on D
  st m <= n & l= n - m
  holds (Op-Right(s,m)) is Element of l-tuples_on D
  proof
    let m,n,l be non zero Element of NAT,
    s be Element of n-tuples_on D;
    assume A1: m <= n & l= n - m;
    len s = n by CARD_1:def 7;
    then len (Op-Right(s,m)) = l by A1,RFINSEQ:def 1;
    then Op-Right(s,m) is Tuple of l,D by CARD_1:def 7;
    hence thesis by FINSEQ_2:131;
  end;
