 heard of SDs. You've heard of vessels. You've heard of ours. You've heard of SRs and SPs and S pluses and S minuses, but have you heard of an SD mine? Oh, I forgot, S deltas. So, but have you heard of an SD minus? I'll tell you what it is. It's really simple. It's just a discriminative stimulus for punishment. That's it. It's just a stimulus that signals that under this condition that when this is present that a behavior is gonna be punished. So, that's really it. Like an SD minus, on our channel, yeah, an SD minus, on our channel we might have referred to that as an STP before. I've seen them written several ways. STPs make sense. Or an SD minus. Take your pick. Signals punishment. That's it.