Axiomatizable theories with few axiomatizable extensions

Abstract

In this paper we prove two theorems. They answer questions raised by Myhill in 1956. (We recall the well-known fact that Myhill's invention of the maximal set in 1956 [2] stemmed from his attempt to prove I below.)I. There exists an axiomatizable, essentially undecidable theory in standard formalization such that all axiomatizable extensions of are finite extensions.II. There exists an axiomatizable but undecidable theory in standard formalization such that(a) has a consistent, complete, decidable extension ,(b) If is an axiomatizable extension of then either(i) is a finite extension of , or(ii) is a finite extension of .