The Four Primary Systems in the Cosmos

I feel like we know the primary system that leads from a reader's perspective which would be the scandrian system. I'm wondering what are the four primary systems that they are talking about because I thought scadrill was one. They're including rishar in the four. Okay and that's named and Bien doll. We don't know what the other two is and yeah we don't know. Let us know what you think if you have another answer for the last of these possible four primary systems, Threnity.