The Collineation Groups of Derived Translation Planes. II. Michael Walker — 1976 Mathematische Zeitschrift
On the Structure of Finite Collineation Groups Containing Symmetries of Generalized Quadrangles. Michael Walker — 1977 Inventiones mathematicae
Perspectivities in Irreducible Collineation Groups of Projective Planes. I. Christoph Hering; Michael Walker — 1977 Mathematische Zeitschrift