Carolyn Chun

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A parallel minor is obtained from a graph by any sequence of edge contractions and parallel edge deletions. We prove that, for any positive integer k, every internally 4-connected graph of sufficiently high order contains a parallel minor isomorphic to a variation of K 4,k with a complete graph on the vertices of degree k, the k-partition triple fan with a(More)
Let M be a matroid. When M is 3-connected, Tutte's Wheels-and-Whirls Theorem proves that M has a 3-connected proper minor N with |E(M) − E(N)| = 1 unless M is a wheel or a whirl. This paper establishes a corresponding result for internally 4-connected binary matroids. In particular, we prove that if M is such a matroid, then M has an internally 4-connected(More)
In our quest to find a splitter theorem for internally 4-connected binary matroids, we proved in the preceding paper in this series that, except when M or its dual is a cubic Möbius or planar ladder or a certain coextension thereof, an internally 4-connected binary matroid M with an internally 4-connected proper minor N either has a proper internally(More)
A sufficiently large connected matroid M contains a big circuit or a big cocircuit. Pou-Lin Wu showed that we can ensure that M has a big circuit or a big cocircuit containing any chosen element of M. In this paper, we begin with a fixed connected matroid N and we take M to be a connected matroid that has N as a minor. Our main result establishes that if M(More)
If S is a set of matroids, then the matroid M is S-fragile if, for every element e ∈ E(M), either M \e or M/e has no minor isomorphic to a member of S. Excluded-minor characterizations often depend, implicitly or explicitly, on understanding classes of fragile matroids. In certain cases, when M is a minor-closed class of S-fragile matroids, and N ∈ M, the(More)