No non-trivial quasivariety of BCK-algebras has decidable first order theory

Using the semantic embedding technique the theorem announced by the title is proved.     

Logic of nondeterministic information

In the paper we define a class of languages for representation o knowledge in those application areas when a complete information about a domain is not available. In the languages we introduce modal operators determined by accessibility relations depending on parameters.     

On comparison of theories by their contents

Popper's definition of verisimilitude was criticized for its paradoxical consequences in the case of false theories. The aim of this paper is to show that paradoxes disappear if the falsity content of a theory is defined with help of dCn or Cn ^–1.To the memory of Jerzy SupeckiI am grateful to David Pearce, Gerhard Schurz, Peter Simons, Maciej Spasowski and Jan Zygmunt for their helpful discussions on issues analysed in this paper. Particularly, Zygmunt's and Spasowski's comments enabled me to correct several mistakes of the earlier drafts.     

Wprowadzanie implikacji na kursach logiki usługowej

Allatum est die 1 Augusti 1969