theorem Th10:
  for D being set holds (for i being Nat st i in dom p holds p.i in D)
  implies p is FinSequence of D
proof
  let D be set;
  assume
A1: for i being Nat st i in dom p holds p.i in D;
  let b be object;
  assume b in rng p;
  then ex i being Nat st i in dom p & p.i = b by Th8;
  hence thesis by A1;
end;
