Association schemes on the set of antiflags of a projective plane (Q1322226)

The author defines an association scheme on the set of antiflags of any projective plane in the obvious way (an antiflag is a non-incident point- line pair), namely by looking at the possible mutual positions of two antiflags: equal, sharing an element, constituting one flag, constituting two flags, lines intersecting on the join of the points and the general position. The author shows that this defines a symmetric primitive rank 6 association scheme, from which the original projective plane can be recovered (up to non-necessarily type-preserving isomorphism).