A remark on the uniqueness of embeddings of linear spaces into desarguesian projective planes

Suppose that q ? 2 is a prime power. We show that a linear space with a(q + 1)² + (q + 1) points, where a ? 0.763, can be embedded in at most one way in a desarguesian projective plane of order q. © 1995 John Wiley & Sons, Inc.     

A Beckman-Quarles type theorem for finite desarguesian planes

The characterization theorem given in [2] for Lorentz transformations of the ² is carried over to the case of finite planes.Dedicated to G. Pickert on the occasion of his 65. birthday.     

Pathological projective planes: Associate affine planes

In [7] the author showed the existence of projective plane pathological with respect to the collineation groups of its sub and quotient planes. Similar pathologies are obtainable with respect to collineation groups of associated affine planes. (i.e. the affine planes obtained by distinguishing a line as the line at infinity) as expressable in the following theorem.     

Hadamard matrices and projective planes

The construction of a Hadamard matrix of order n² from a projective plane of order n, n even, is given. Alternative constructions, specialized to the case n = 10, from sets of mutually orthogonal Latin squares are also given. Special properties of the Hadamard matrices are discussed and a partial example is given in the case n = 10.     

Constructively presented projective planes

An attempt to define a finite presentation for projective planes by analogy to finitely presented groups has been made in [9]. In this article we suggest another definition for a presentation of projective planes: constructively presented planes. A few simple results about such planes and an example of constructively presented planes with nonsolvable word problem are given.This paper was written while the author was visiting the University of Bergen, Norway.     

Stable periodic projective planes

We find all stable projective planes with finite topology which are properly embedded in , where is a discrete subgroup of translations in . Here stable means second order minimum of the area. The surfaces we obtain are a quotient of the helicoid and quotients of the doubly periodic Scherk surfaces.

     

Minimal topological projective planes

The atoms of the lattice of compatible topologies on a given projective plane are examined. The notion of a field of type V is generalized to ternary fields of type V. These are always minimal, and they arise for example as coordinate structure of strictly uniformizable or of orderable topological planes. Hence, such planes are minimal.Dedicated to Professor Helmut Karzel on his 60^th birthday