Groups with a recursively enumerable irreducible word problem

The notion of the word problem is of fundamental importance in group theory. The irreducible word problem is a closely related concept and has been studied in a number of situations; however there appears to be little known in the case where a finitely generated group has a recursively enumerable irreducible word problem. In this paper we show that having a recursively enumerable irreducible word problem with respect to every finite generating set is equivalent to having a recursive word problem. We prove some further results about groups having a recursively enumerable irreducible word problem, amongst other things showing that there are cases where having such an irreducible word problem does depend on the choice of finite generating set

Argumentation Theory for Mathematical Argument

To adequately model mathematical arguments the analyst must be able to represent the mathematical objects under discussion and the relationships between them, as well as inferences drawn about these objects and relationships as the discourse unfolds. We introduce a framework with these properties, which has been used to analyse mathematical dialogues and expository texts. The framework can recover salient elements of discourse at, and within, the sentence level, as well as the way mathematical content connects to form larger argumentative structures. We show how the framework might be used to support computational reasoning, and argue that it provides a more natural way to examine the process of proving theorems than do Lamport's structured proofs.Comment: 44 pages; to appear in Argumentatio

Descriptions of Groups using Formal Language Theory

This work treats word problems of finitely generated groups and variations thereof, such as word problems of pairs of groups and irreducible word problems of groups. These problems can be seen as formal languages on the generators of the group and as such they can be members of certain well-known language classes, such as the class of regular, one-counter, context-free, recursively enumerable or recursive languages, or less well known ones such as the class of terminal Petri net languages. We investigate what effect the class of these various problems has on the algebraic structure of the relevant group or groups. We first generalize some results on pairs of groups, which were previously proven for context-free pairs of groups only. We then proceed to look at irreducible word problems, where our main contribution is the fact that a group for which all irreducible word problems are recursively enumerable must necessarily have solvable word problem. We then investigate groups for which membership of the irreducible word problem in the class of recursively enumerable languages is not independent of generating set. Lastly, we prove that groups whose word problem is a terminal Petri net language are exactly the virtually abelian groups