Section 3.2 of Coxeter's Projective Geometery discusses the self-dual $10_3$ configuration, ten points and ten lines, with three pointson each line and three lines through each point.
I am looking at the Figure 2.3a, but I am having trouble trying to find $P_1S$, where are the "exterior" points.
Could someone please tell me of a link, book, or at all else draw or clearly explain where these points line?