A nonpermutational integral relation algebra
The authors, starting from a problem raised by McKenzie, show that there are infinitely many nonpermutational integral relation set algebras such that a nonprincipal ultraproduct of these is permutable. They infer that the class of all permutational relation algebras is not finitely axiomatizable over the class of all integral relation set algebras. The paper is remarkably self-contained.
nonpermutational integral relation set algebras
scientific article; zbMATH DE number 222023