reserve i,j,k,l for natural Number;
reserve A for set, a,b,x,x1,x2,x3 for object;
reserve D,D9,E for non empty set;
reserve d,d1,d2,d3 for Element of D;
reserve d9,d19,d29,d39 for Element of D9;
reserve p,q,r for FinSequence;
reserve s for Element of D*;

theorem
  idseq i is Element of i-tuples_on NAT
proof
  idseq i is FinSequence of NAT & len idseq i = i by Th46,CARD_1:def 7;
  hence thesis by Th90;
end;
