Department of Mathematics

University of Illinois at Urbana-Champaign

1409 W. Green Street (MC-382)

Urbana, Illinois 61801-2975

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Office: 353 Altgeld Hall
Phone: (217) 333-1610
Fax: (217) 333-9576
e-mail: **

**Area of interest and specialization:**

**Selected Publications**

(with R.C. Lyndon), Combinatorial group theory (Reprint of the 1977 edition). In *Classics in Mathematics*, Springer-Verlag, Berlin (2001).

(with S. Ivanov), A remark on finitely generated subgroups of free groups. In *Algorithmic Problems in Groups and Semigroups* (J.-C. Birget, S. Margolis, J. Meakin, M. Sapir, Eds.), Birhäuser, Boston (2000) 139-142.

(with D. Beauquier and D. Muller), The bar problem -- a simple tiling problem which is NP-complete on the Euclidean tessellation by squares but which is polynomial time on hyperbolic tesselations by *4g*-gons. In *Groups, Languages and Geometry* (R. Gilman, Ed.), Comtemporary Mathematics, Vol. 250, American Mathematical Society (1999) 29--36.

(with C.F. Miller, III), Some presentations of the trivial group. In *Groups, Languages and Automata* (R. Gilman, Ed.), Contemporary Mathematics, Vol. 250, American Mathematical Society (1999) 113--115.

(with S. Ivanov), On the hyperbolicity of small cancellation groups and one-relator groups,* Trans. Amer. Math. Soc.* 350 (1998) 1851--1894.

On the structure of Hamiltonian cycles in the Cayley graphs of finite quotients of the modular group,* Theoretical Comput. Sci.* 204 (1998) 233--248.

Last modified May 22, 2001