24 research outputs found
Complexity of equational theory of relational algebras with standard projection elements
The class of t rue p airing a lgebras is defined to be the class of relation algebras expanded with concrete set theoretical projection functions. The main results of the present paper is that neither the equational theory of nor the first order theory of are decidable. Moreover, we show that the set of all equations valid in is exactly on the level. We consider the class of the relation algebra reducts of ’s, as well. We prove that the equational theory of is much simpler, namely, it is recursively enumerable. We also give motivation for our results and some connections to related work