Mathematics – Combinatorics
Scientific paper
2011-11-02
Mathematics
Combinatorics
24 pages, 4 figures, submitted
Scientific paper
We introduce the \emph{nearly finitary} matroids which form a superclass of the finitary matroids, and prove that the union of two nearly finitary matroids is a matroid and, in fact, nearly finitary. To prove the latter, we appeal to the finitary matroid union theorem established in the first paper of this series. We also characterize the nearly finitary graphic matroids. Using the nearly finitary matroid union result, we establish that the \emph{infinite matroid intersection conjecture} of Nash-Williams is true whenever the first matroid is nearly finitary and the second is the dual of a nearly finitary matroid. From this we derive an alternative matroidal proof of the infinite Menger theorem for locally finite graphs. In addition, we show that the infinite matroid intersection conjecture for finitary implies the general infinite Menger theorem which was conjectured by Erd\H{o}s, and proved only recently by Aharoni and Berger.
Aigner-Horev Elad
Carmesin Johannes
Fröhlich Jan-Oliver
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