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Polar Graphs and Corresponding Involution Sets, Loops and Steiner Triple Systems
Authors:Helmut Karzel  Silvia Pianta  Elena Zizioli
Institution:(1) Zentrum Mathematik, T.U. München, D-80290 München, Germany;(2) Dipartimento di Matematica e Fisica, Università Cattolica, Via Trieste, 17, I-25121 Brescia, Italy;(3) Dipartimento di Matematica, Facoltà di Ingegneria, Università degli Studi di Brescia, Via Valotti, 9, I-25133 Brescia, Italy
Abstract:A 1-factorization (or parallelism) of the complete graph with loops $$(P, \mathcal{E}, ||)$$ is called polar if each 1-factor (parallel class) contains exactly one loop and for any three distinct vertices x1, x2, x3, if {x1} and {x2, x3} belong to a 1-factor then the same holds for any permutation of the set {1, 2, 3}. To a polar graph $$ (P, \mathcal{E}, ||)$$ there corresponds a polar involution set $$ (P, \mathcal{I})$$ , an idempotent totally symmetric quasigroup (P, *), a commutative, weak inverse property loop (P, + ) of exponent 3 and a Steiner triple system $$ (P, \mathcal{B})$$ . We have: $$ (P, \mathcal{E}, ||)$$ satisfies the trapezium axiom $$ \Leftrightarrow \forall \alpha \in \mathcal{I}: \alpha \mathcal{I}\alpha = \mathcal{I} \Leftrightarrow (P,*) $$ is self-distributive ⇔ (P, + ) is a Moufang loop $$ \Leftrightarrow (P, \mathcal{B})$$ is an affine triple system; and: $$ (P, \mathcal{E}, ||)$$ satisfies the quadrangle axiom $$ \Leftrightarrow \mathcal{I}^{3} = \mathcal{I} \Leftrightarrow (P, + ) $$ is a group $$ \Leftrightarrow (P, \mathcal{B})$$ is an affine space.
Keywords:20N05  05C70  51E10
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