We show that CC-circuits of bounded depth have the same expressive power as circuits over finite nilpotent algebras from congruence modular varieties. We use this result to phrase and discuss a new algebraic version of Barrington, Straubing and Th\'erien's conjecture, which states that CC-circuits of bounded depth need exponential size to compute AND. Furthermore, we investigate the complexity of deciding identities and solving equations in a fixed nilpotent algebra. Under the assumption that the conjecture is true, we obtain quasipolynomial algorithms for both problems. On the other hand, if AND is computable by uniform CC-circuits of bounded depth and polynomial size, we can construct a nilpotent algebra in which checking identities is coNP-complete, and solving equations is NP-complete.

@article{paperbot1699,
  title = {CC-circuits and the expressive power of nilpotent algebras},
  author = {Michael Kompatscher},
  journal = {Logical Methods in Computer Science},
  volume = {Volume 18, Issue 2},
  year = {2022},
  doi = {10.46298/lmcs-18(2:12)2022}
}