"We prove that any variety of relation algebras which contains an algebra with infinitely many elements below the identity, or which contains the full group relation algebra on some infinite group (or on arbitrarily large finite groups), must have an undecidable equational theor…
In part I we address the question: which varieties have a decidable first order theory? We confine our attention to varieties whose algebras have modular congruence lattices (i.e., modular varieties), and focus primarily on locally finite varieties, although near the end of the …
Forever Undecided is the most challenging yet of Raymond Smullyan's puzzle collections. It is, at the same time, an introduction'ingenious, instructive, entertaining'to GOdel's famous theorems. With all the wit and charm that have delighted readers of his previous books, Smullya…
