Flag-transitive Steiner Designs

• Incidence Structures and Steiner Designs.- Permutation Groups and Group Actions.- Number Theoretical Tools.- Highly Symmetric Steiner Designs.- A Census of Highly Symmetric Steiner Designs.- The Classification of Flag-transitive Steiner Quadruple Systems.- The Classification of Flag-transitive Steiner 3-Designs.- The Classification of Flag-transitive Steiner 4-Designs.- The Classification of Flag-transitive Steiner 5-Designs.- The Non-Existence of Flag-transitive Steiner 6-Designs.

This monograph provides an excellent development of the existence and nonexistence of flag-transitive and other symmetric Steiner t-designs. In particular, it develops a complete classification of all flag-transitive Steiner t-designs for strength t at least three. The topic is a beautiful mixture of algebra and combinatorics, and it impinges on many applications areas. Of particular value is the material providing the necessary background in group theory, incidence geometry, number theory, and combinatorial design theory to support a complete exposition of the many results. These form the focus of the first three chapters. Chapter 4 then develops results on symmetric actions of groups on Steiner systems, and provides many helpful examples. Chapter 5 then states the main existence result for flag-transitive Steiner systems, and places this in the context of related existence results for highly symmetric actions. Chapters 6 through 10 fill in the details of the existence proof. Steiner quadruple systems are treated in Chapter 6, while strength three in general is treated in Chapter 7. Chapters 8 and 9 then treat the cases of strengths four and five, respectively. Finally Chapter 10 provides the proof that no flag-transitive Steiner 6-design exists. The presentation is lucid and accessible. Indeed the author has done a first rate job of presenting material that involves many deep ideas and a number of technical issues. At the same time, the monograph indicates useful next steps to take in the research topic. Zentralblatt Math - Charles J. Colbourn (Tempe)