Output

MoveNext: True
MoveNext: False
MoveNext: True
MoveNext: False

Reentrant Enumerator.cs

static IEnumerator e;
static void Main() {
 	e = M();
  	Console.WriteLine("MoveNext: " + e.MoveNext());
  	Console.WriteLine("MoveNext: " + e.MoveNext());
  	Console.WriteLine("MoveNext: " + e.MoveNext());
}

static IEnumerator M() {
  yield return 3;
  Console.WriteLine("MoveNext: " + e.MoveNext());
  yield return 4;
}