reserve N,M,K for ExtNat;
reserve X for ext-natural-membered set;

theorem
  for D being non empty set, p being non empty trivial Sequence of D
  ex x being Element of D st p = <% x %>
proof
  let D be non empty set, p be non empty trivial Sequence of D;
  consider x being object such that
    A1: p = <% x %> by Th9;
  rng p = {x} by A1, AFINSQ_1:33;
  then x in rng p by TARSKI:def 1;
  then reconsider x as Element of D;
  take x;
  thus thesis by A1;
end;
