It's a private function that gets called *a lot* (I suspect it's the primary bottleneck), and the one place it's used I ensure that it is only used for n > 1. I put this in as a note more to protect us in case anything else wanted to use the function later. But maybe the assert wouldn't add too much time... in any case, it hopefully won't matter because I'm going to see if it's possible to avoid using this function at all.