The Veronese Surface in PG(5,3) and Witt's 5-$(12,6,1$ Design

Abstract

A conic of the Veronese surface in PG(5,3) is a quadrangle. If one such quadrangle is replaced with its diagonal triangle, then one obtains a point model $K$ for Witt's 5-$(12,6,1)$ design, the blocks being the hyperplane sections containing more than three (actually six) points of $K$. As such a point model is projectively unique, the present construction yields an easy coordinate-free approach to some results obtained independently by H.S.M. Coxeter and G. Pellegrino, including a projective representation of the Mathieu group $M_{12}$ in PG(5,3).