
theorem
  for D being non empty set for f being non empty FinSequence of D, g
  being FinSequence of D holds (g^f)/.len(g^f) = f/.len f
proof
  let D be non empty set, f be non empty FinSequence of D, g be FinSequence of
  D;
A1: len f >= 1 by NAT_1:14;
  len(g^f) = len g + len f by FINSEQ_1:22;
  hence thesis by A1,SEQ_4:136;
end;
