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On the combinatorics of Galois numbers. (English) Zbl 1226.11030

The Galois number \(G_n^q\) is the total number of linear subspaces of \(\text{GF}(q)^n\). Is it possible to partition the lattice of subspaces of \(\text{GF}(q)^n\) into two intervals of length \(n-1\) and \(q^{n-1}-1\) intervals of length \(n-2\), for \(n\geq 2\)? The authors consider such interval decompositions for vector spaces \({\mathbb F}^n\) of finite dimension over arbitrary fields \({\mathbb F}\) and show that the existence of such a decomposition is equivalent to the existence of so called pointwise irreflexive and antisymmetric linear forms. This implies that for \(n\geq 3\) an interval decomposition of \({\mathbb F}^n\) exists only if \({\mathbb F}^{n-1}\) admits an interval decomposition. They show that \({\mathbb R}^n\) has an interval decomposition, while \(\text{GF}(2)^n\) has an interval decomposition if and only if \(n\leq 4\). They present an interval decomposition of \(\text{GF}(3)^5\).

MSC:

11B75 Other combinatorial number theory
05A18 Partitions of sets
11T30 Structure theory for finite fields and commutative rings (number-theoretic aspects)
Full Text: DOI

References:

[1] Ulrich Faigle, personal communication, 2004.; Ulrich Faigle, personal communication, 2004.
[2] Goldman, Jay; Rota, Gian-Carlo, The number of subspaces of a vector space, Recent Progress in Combinatorics (Proc. Third Waterloo Conf. on Combinatorics, 1968) (1969), Academic Press: Academic Press New York, 75-83 · Zbl 0196.02801
[3] Steffen Hitzemann, Über die Kombinatorik der Galoiszahlen, Master’s thesis, FernUniversität in Hagen, October 2008, p. 109.; Steffen Hitzemann, Über die Kombinatorik der Galoiszahlen, Master’s thesis, FernUniversität in Hagen, October 2008, p. 109.
[4] Eva Kruse, Symmetrische Kettenzerlegungen von Verbänden und Intervallzerlegung des linearen Verbandes, Master’s thesis, Universität zu Köln, August 2004, p. 107.; Eva Kruse, Symmetrische Kettenzerlegungen von Verbänden und Intervallzerlegung des linearen Verbandes, Master’s thesis, Universität zu Köln, August 2004, p. 107.
[5] Schrijver, Alexander, Combinatorial Optimization: Polyhedra and Efficiency (2004), Springer, July · Zbl 1072.90030
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