Characterization of complete exterior sets of conics


Let ε be a set of\(\frac{{q + 1}}{2}\) exterior points of a nondegenerate conic inPG(2,q) with the property that the line joining any 2 points in ε misses the conic. Ifq≡1 (mod 4) then ε consists of the exterior points on a passant, ifq≡3 (mod 4) then other examples exist (at least forq=7, 11, ..., 31).

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Support from the Dutch organization for scientific Research (NWO) is gratefully acknowledged

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Blokhuis, A., Seress, Á. & Wilbrink, H.A. Characterization of complete exterior sets of conics. Combinatorica 12, 143–147 (1992).

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AMS subject classification code (1991)

  • 05 B 25
  • 51 E 15