 reserve x for Real,
    p,k,l,m,n,s,h,i,j,k1,t,t1 for Nat,
    X for Subset of REAL;
reserve x for object, X,Y,Z for set;
 reserve M,N for Cardinal;
reserve X for non empty set,
  s for sequence of X;

theorem
  s.n in rng s
proof
  n in NAT by ORDINAL1:def 12;
  then n in dom s by FUNCT_2:def 1;
  hence thesis by FUNCT_1:3;
end;
