
doi: 10.1002/jcd.20260
handle: 11563/19480
In this very interesting paper, the authors look at some intricate questions related to subconfigurations of certain generalised quadrangle (GQs). These GQs are of order \((s,t)\) and are constructed as \({\mathbf H(3, q^2)}\), the incidence structure of all the points and lines of a Hermitian surface in \(PG(3, q^2)\). A subquadrangle regular system of order \(m\) on a GQ of order \((s, t)\) is a set \textbf{R} of embedded subquadrangles with the property that every point lies on exactly \(m\) subquadrangles (where \(m\) is a fixed natural number) and if \(m\) is half of the total number of subquadrangles on a point, then \textbf{R} is called a subquadrangle hemisystem. This generalizes the notion of hemisystem that was first looked at by Segre (where lines were considered instead of subquadrangles). The paper under review which has a lot of nice results constructs two infinite families of symplectic subquadrangle hemisystems of \({\mathbf H(3, q^2)}\), where \(q\) is an odd prime admitting \(P{\Omega}^{\pm}_4(q)\) as an automorphism group. The paper also constructs two infinite families of symplectic subquadrangle hemisystems of \(W_3(q^2)\), \(q\) even, admitting the group \(PSL(2, q^2)\) as an automorphism group. The paper also presents some sporadic examples of subquadrangle regular systems of \({\mathbf H(3, q^2)}\).
subquadrangle hemisystems, subquadrangle regular system, Linear algebraic groups over finite fields, symplectic polarity, generalized quadrangle, Combinatorial structures in finite projective spaces, Generalized quadrangles and generalized polygons in finite geometry, Hermitian surface, unitary polarity, subquadrangles
subquadrangle hemisystems, subquadrangle regular system, Linear algebraic groups over finite fields, symplectic polarity, generalized quadrangle, Combinatorial structures in finite projective spaces, Generalized quadrangles and generalized polygons in finite geometry, Hermitian surface, unitary polarity, subquadrangles
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