theorem Th29:
  x in rng p implies 1 in dom p
proof
  assume x in rng p;
  then p <> {};
  then
A1: 1 <= len p by NAT_1:14;
  dom p = Seg(len p) by FINSEQ_1:def 3;
  hence thesis by A1,FINSEQ_1:1;
end;
