The Andrews-Curtis Conjecture, Term Rewriting and First-Order Proofs

The Andrews-Curtis conjecture (ACC) remains one of the outstanding open problems in combinatorial group theory. In short, it states that every balanced presentation of the trivial group can be transformed into a trivial presentation by a sequence of simple transformations. It is generally believed that the conjecture may be false and there are several series of potential counterexamples for which required simplifications are not known. Finding simplifications poses a challenge for any computational approach - the search space is unbounded and the lower bound on the length of simplification sequences is known to be at least superexponential. Various specialised search algorithms have been used to eliminate some of the potential counterexamples. In this paper we present an alternative approach based on automated reasoning. We formulate a term rewriting system ACT for AC-transformations, and its translation(s) into the first-order logic. The problem of finding AC-simplifications is reduced to the problem of proving first-order formulae, which is then tackled by the available automated theorem provers. We report on the experiments demonstrating the efficiency of the proposed method by finding required simplifications for several new open cases

All simple groups with order from 1 million to 5 million are efficient

There is much interest in finding short presentations for the finite simple groups. Indeed it has been suggested that all these groups are efficient in a technical sense. In previous papers we produced nice efficient presentations for all except one of the simple groups with order less than one million. Here we show that all simple groups with order between 1 million and 5 million are efficient by giving efficient presentations for all of them. Apart from some linear groups these results are all new. We also show that some covering groups and some larger simple groups are efficient We make substantial use of systems for computational group theory and, in particular, of computer implementations of coset enumeration to find and verify our presentations