reserve a,a1,a2,v,v1,v2,x for object;
reserve V,A for set;
reserve m,n for Nat;
reserve S,S1,S2 for FinSequence;

theorem Th2:
  for f being Function st dom f = NAT holds f|Seg(n) is FinSequence
  proof
    let f be Function;
    assume dom f = NAT;
    then dom(f|Seg(n)) = Seg n by RELAT_1:62;
    hence thesis by FINSEQ_1:def 2;
  end;
