reserve i,j,k,n for Nat;
reserve D for non empty set,
  p for Element of D,
  f,g for FinSequence of D;

theorem
  p in rng Ins(f,n,p)
proof
  p in {p} by TARSKI:def 1;
  then p in {p} \/ rng f by XBOOLE_0:def 3;
  hence thesis by Th70;
end;
