Archiv der Mathematik

, Volume 78, Issue 2, pp 166–172 | Cite as

A combinatorial characterization of classical unitals

  • A. Aguglia
  • G. L. Ebert


In this paper we give a characterization of classical unitals in terms of a configuration pattern formed by the feet of a unital U embedded in PG(2, q 2), q > 2. We show that a necessary and sufficient condition for U to be classical is the existence of two points \( p_0, p_1 \in U \) with tangent lines L 0 and L 1, respectively, such that for all points \( r \in L_0 \backslash \{p_0\} \) and \( s \in L_1 \backslash \{p_1\} \) the corresponding feet are collinear.


Tangent Line Classical Unitals Combinatorial Characterization Configuration Pattern 
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Copyright information

© Birkhäuser Verlag, Basel 2002

Authors and Affiliations

  • A. Aguglia
    • 1
  • G. L. Ebert
    • 2
  1. 1.Dipartimento di Mat. e Appl., “R. Caccioppoli”, Università di Napoli “Federico II”, 80126 Napoli, Italy, e-mail: aguglia@matna2.dma.unina.itIT
  2. 2.Department of Mathematical Sciences, University of Delaware, Newark, DE 19716, USA,¶ e-mail: ebert@math.udel.eduUS

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