reserve f for Function;
reserve n,k,n1 for Element of NAT;
reserve r,p for Complex;
reserve x,y for set;
reserve seq,seq1,seq2,seq3,seq9,seq19 for Complex_Sequence;

theorem
  for r ex seq st rng seq={r}
proof
  let r;
  consider f such that
A1: dom f=NAT and
A2: rng f={r} by FUNCT_1:5;
  for x being object st x in {r} holds x in COMPLEX
      by XCMPLX_0:def 2;
  then rng f c= COMPLEX by A2,TARSKI:def 3;
  then reconsider f as Complex_Sequence by A1,FUNCT_2:def 1,RELSET_1:4;
  take f;
  thus thesis by A2;
end;
