reserve p,q,r for FinSequence;
reserve u,v,x,y,y1,y2,z for object, A,D,X,Y for set;
reserve i,j,k,l,m,n for Nat;

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;
