Tue, 8 Oct 2024, 12:00 pm MDT
We want to study the class of all finite structures together with the preorder given by primitive positive constructions as it plays an important role in the theory of constraint satisfaction problems. It is also equivalent to the homomorphism poset of the polymorphism minion of the structure, which is the right generalization of endomorphism monoid/ring in this context.
It turns out that the first two layers of this order consist of a single equivalence class each, while the third layer consists of infinitely many points, represented by the transitive tournament on three vertices and structures in one-to-one correspondence with all finite simple groups.