A Collapse Result for Constraint Queries over Structures of Small Degree

Collapse results, which are central for understanding constraint database queries, show that in terms of the expressive power, a large class of queries collapses to a much smaller one, typically involving only a restricted form of quanti cation. Most collapse results have been proved over constraints involving a linear order, and proofs are typically rather nontrivial. In this short note we give an easy proof of a powerful form of collapse for a large class of constraints without a linear order, namely those in which all basic relations are of small degree