On aspherical presentations of groups.
On exponential growth rates for free groups.
Let Fp be a free group of rank p ≥ 2. It is well-known that, with respect to a p-element generating set, that is, a basis, the exponential growth rate of Fp is 2p-1. We show that the exponential growth rate τ of a group G with respect to a p-element generating set X is 2p-1 if and only if G is free on X; otherwise τ < 2p-1. We also prove that, for any finite generating set X of Fp which is disjoint from X-1, the exponential growth rate τ of Fp with respect to X is 2p-1 if and only if X is...
On infinite Nielsen transformations.
On the Burnside problem for groups of even exponent.
On the SQ-universality of T(6)-groups.
On Tits' conjecture and other questions concerning Artin and generalized Artin groups.