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Published online by Cambridge University Press: 20 November 2018
A well-known result of Dembowski and Wagner (4) characterizes the designs of points and hyperplanes of finite projective spaces among all symmetric designs. By passing to a dual situation and approaching this idea from a different direction, we shall obtain common characterizations of finite projective and affine spaces. Our principal result is the following.
Theorem 1. A finite incidence structure is isomorphic to the design of points and hyperplanes of a finite projective or affine space of dimension greater than or equal to4 if and only if there are positive integers v, k, and y, with μ > 1 and (μ – l)(v — k) ≠ (k — μ)2such that the following assumptions hold.
(I) Every block is on k points, and every two intersecting blocks are on μ common points.
(II) Given a point and two distinct blocks, there is a block containing both the point and the intersection of the blocks.
(III) Given two distinct points p and q, there is a block on p but not on q.
(IV) There are v points, and v– 2 ≧ k > μ.