Absorption in finitely related SD(meet) algebras has bounded arity
The notion of absorbing subuniverse plays an important role in the recent development of the algebraic approach to CSP and finite universal algebra in general. Our result addresses absorption in finitely related SD(∧) algebras. Let A be a finite finitely related algebra in a congruence meet-semidistributive variety. Assume that the relational clone corresponding to A is generated by at most n-ary relations. We prove that whenever B is an absorbing subuniverse of A, there exists t ∈ Clo(A) of arity 48 |A| n + 1 such that B absorbs A with respect to t. As a consequence, we obtain a partial answer to a question by Barto: Given a finite relational structure A, and a subset B ⊆ A, is it decidable if B is an absorbing subuniverse? Our result yields a positive answer in the case when the algebra of polymorphisms of A is an SD(∧) algebra.