Prof. Johan Böhm

Prof. Dr. Prof. Prof.

Regular Böhm trees

Böhm trees are the natural infinite generalisations of normal forms in pure λ-calculus. They arose from the work of Böhm on separability (Böhm 1968), and were first identified by Barendregt, who devotes chapter 10 of his book (Barendregt 1980) to their study, and relates denotational models such as D∞ to appropriate quotients over Böhm trees. There is however no generally agreed presentation of...

Computing with Böhm Trees

This paper develops a general technique to analyze the head reduction of a term in a context. This technique is used to give a direct proof of the theorem of Hyland and Wadsworth : two -terms that have the same Böhm trees, up to (possibly infinite) -equivalence, are operationally equivalent. It is also used to prove a conjecture of R. Kerth : Every unsolvable -term has a decoration. This syntac...

An Extensional Böhm Model

We show the existence of an infinitary confluent and normalising extension of the finite extensional lambda calculus with beta and eta. Besides infinite beta reductions also infinite eta reductions are possible in this extension, and terms without head normal form can be reduced to bottom. As corollaries we obtain a simple, syntax based construction of an extensional Böhm model of the finite la...

Johan Petersson

This paper presents a tentative framework for understanding a particular environment of electronic commerce activities the local electronic marketplace. This type of marketplace is Internet-based and dedicated to consumer-oriented commerce. The framework consists of two main components: marketplace functions and marketplace practice. Viewing an electronic marketplace in this way means adopting ...