By Michael Huber

The monograph presents the 1st complete dialogue of flag-transitive Steiner designs. this can be a critical a part of the examine of hugely symmetric combinatorial configurations on the interface of a number of mathematical disciplines, like finite or prevalence geometry, workforce thought, combinatorics, coding concept, and cryptography. In a sufficiently self-contained and unified demeanour the type of all flag-transitive Steiner designs is gifted. This fresh consequence settles attention-grabbing and not easy questions which were item of analysis for greater than forty years. Its evidence combines tools from finite crew conception, prevalence geometry, combinatorics, and quantity theory.

The e-book includes a vast advent to the subject, in addition to many illustrative examples. in addition, a census of a few of the main basic effects on hugely symmetric Steiner designs is given in a survey chapter.

The monograph is addressed to graduate scholars in arithmetic and desktop technology in addition to proven researchers in layout conception, finite or occurrence geometry, coding conception, cryptography, algebraic combinatorics, and extra more often than not, discrete mathematics.

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**Example text**

Because of the transitivity of GB on the points of B, we conclude that k |GB | 2d. 14 (c). / B. Let G∗ = Now, let TB = 1. We ﬁrst show that GB ≤ Gy for some y ∈ ∗ GB ∩ AGL(1, v). Then G is conjugate to a subgroup of G0 by Hall’s theorem. If G∗ = 1, then GB is isomorphic to a subgroup of α , hence cyclic and |GB | d. 1). The very few possibilities for k can easily be ruled out by hand as before. Therefore, G∗ = 1. By construction, G∗ has only the point 0 as ﬁxed point. , the / B by the ﬂag-transitivity of G.

N n This leaves only a small number of cases to check. 17. Case (2): G0 ☎ SL( ad , pa ), d ≥ 2a. Let ei denote the i-th standard basis vector of the vector space V = V ( ad , pa ), and ei the 1-dimensional vector subspace spanned by ei . 1 with d ≥ 3 and G∼ = AGL(d, 2) can occur. First, let pa = 2. For d = 2a, let U = U ( e1 ) ≤ G0 denote the subgroup of all transvections with axis e1 . Then U consists of all elements of the form 1 0 c 1 , c ∈ GF (pa ) arbitrary. Clearly, U ﬁxes as points only the elements of e1 .

Setting D consists of repeated rows of D. Let α and β denote the linear maps induced by A and U , respectively. Since α(Rn ) = α(β(Rr )) + α(β(Rr )⊥ ) and dim(β(Rr )⊥ ) = n − r, it follows that rank(A) ≤ rank(D) + n − r. As clearly rank(D) ≤ s, the claim is established. 24 Chapter 4. Highly Symmetric Steiner Designs Tactical decompositions may be applied to get inside the orbit structures of groups of automorphisms of incidence structures. 11. Let D = (X, B, I) be an incidence structure with incidence matrix A of rank |X| over R and G ≤ Aut(D) a group of automorphisms of D.