Classification of Moduli Spaces of Arrangements of 9 Projective Lines

In this paper, we present a proof that the list of the classification of arrangements of 9 lines by Nazir and Yoshinaga is complete.Comment: Changed notations in the definition of moduli space to improve clarity. Results unchange

Improvement of inequalities for the (r,q)(r,q)-structures and some geometrical connections

summary:The main results are the inequalities (1) and (6) for the minimal number of $(r,q)$-structure classes,which improve the ones from [3], and also some geometrical connections, especially the inequality (13)

Lines, Circles, Planes and Spheres

Let $S$ be a set of $n$ points in $\mathbb{R}^3$, no three collinear and not all coplanar. If at most $n-k$ are coplanar and $n$ is sufficiently large, the total number of planes determined is at least $1 + k \binom{n-k}{2}-\binom{k}{2}(\frac{n-k}{2})$. For similar conditions and sufficiently large $n$, (inspired by the work of P. D. T. A. Elliott in \cite{Ell67}) we also show that the number of spheres determined by $n$ points is at least $1+\binom{n-1}{3}-t_3^{orchard}(n-1)$, and this bound is best possible under its hypothesis. (By $t_3^{orchard}(n)$, we are denoting the maximum number of three-point lines attainable by a configuration of $n$ points, no four collinear, in the plane, i.e., the classic Orchard Problem.) New lower bounds are also given for both lines and circles.Comment: 37 page

A generalisation of Sylvester's problem to higher dimensions

In this article we consider $S$ to be a set of points in $d$-space with the property that any $d$ points of $S$ span a hyperplane and not all the points of $S$ are contained in a hyperplane. The aim of this article is to introduce the function $e_d(n)$, which denotes the minimal number of hyperplanes meeting $S$ in precisely $d$ points, minimising over all such sets of points $S$ with $|S|=n$.Postprint (published version