reserve
  a for natural Number,
  k,l,m,n,k1,b,c,i for Nat,
  x,y,z,y1,y2 for object,
  X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for FinSequence;
reserve D for set;
reserve a, b, c, d, e, f for object;

theorem Th88:
 for f being n-element FinSequence holds dom f = Seg n
  proof let f be n-element FinSequence;
    len f = n by CARD_1:def 7;
   hence dom f = Seg n by Def3;
  end;
