theorem Th43:
  for f,g be FinSequence st f^g is FinSequence-yielding
    holds f is FinSequence-yielding & g is FinSequence-yielding
proof
  let f,g be FinSequence such that A1: f^g is FinSequence-yielding;
  A2:now let x be object;
    A3:dom f c= dom (f^g) by FINSEQ_1:26;
    assume x in dom f;
    then f.x = (f^g).x & x in dom (f^g) by A3,FINSEQ_1:def 7;
    hence f.x is FinSequence by A1;
  end;
  now let x be object;
    assume A4:x in dom g;
    then reconsider xx=x as Nat;
    g.x = (f^g).(xx+len f) by A4,FINSEQ_1:def 7;
    hence g.x is FinSequence by A1;
  end;
  hence thesis by A2,PRE_POLY:def 3;
end;
