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On (k,n)-arcs and the falsity of the Lunelli-Sce conjecture

Published online by Cambridge University Press:  05 April 2013

R. Hill
Affiliation:
University of Salford
J.R.M. Mason
Affiliation:
University of Salford
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Summary

INTRODUCTION

A (k,n)-arc in PG(2,q) is a set of k points, such that some n, but no n+1, of them are collinear. The maximum value of k for which a (k,n)-arc exists in PG(2,q) will be denoted by m (n)2,q - Clearly m(l)2,q = 1 and m(q+l)2,q = q2 + q + 1, and so from now on we assume that 2 ≤ n ≤ q.

The following two theorems are well-known, and proofs may be found in Chapter 12 of Hirschfeld [12].

THEOREM 1.1:

  1. (i) m(n)2,q ≤ (n-l)q + n.

  2. (ii) (Cossu [8]). For n≤q, equality can occur in (i) only if n | q.

A ((n-l)q + n, n)-arc is known as a maximal arc.

THEOREM 1.2: There exists a maximal arc in PG(2,q) when

(i) n = q, for any q, a maximal arc being the complement of a line,

(ii) (Denniston [10]). q = 2h, and n is any divisor of q.

It is not known whether maximal arcs exist when q is odd and 2 ≤ n < q, although it has been proved by Thas [16] that there are no (2q+3, 3)- arcs in PG(2, 3h) for h > 1.

Type
Chapter
Information
Finite Geometries and Designs
Proceedings of the Second Isle of Thorns Conference 1980
, pp. 153 - 168
Publisher: Cambridge University Press
Print publication year: 1981

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