reserve a,b,i,j,k,l,m,n for Nat;

theorem Th0:
  for f be FinSequence holds ex D be non empty set st f is FinSequence of D
  proof
    let f be FinSequence;
    f is FinSequence of rng f \/ {1} by XBOOLE_1:7,FINSEQ_1:def 4;
    hence thesis;
  end;
