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Full-Text Articles in Physical Sciences and Mathematics
A Novel Proof Of The Heine-Borel Theorem, Matthew Macauley, Brian Rabern, Landon Rabern
A Novel Proof Of The Heine-Borel Theorem, Matthew Macauley, Brian Rabern, Landon Rabern
Publications
Every beginning real analysis student learns the classic Heine-Borel theorem, that the interval [0,1] is compact. In this article, we present a proof of this result that doesn't involve the standard techniques such as constructing a sequence and appealing to the completeness of the reals. We put a metric on the space of infinite binary sequences and prove that compactness of this space follows from a simple combinatorial lemma. The Heine-Borel theorem is an immediate corollary.
Equivalences On Acyclic Orientations, Matthew Macauley, Henning S. Mortveit
Equivalences On Acyclic Orientations, Matthew Macauley, Henning S. Mortveit
Publications
The cyclic and dihedral groups can be made to act on the set Acyc(Y ) of acyclic orientations of an undirected graph Y , and this gives rise to the equivalence relations ∼κ and ∼δ, respectively. These two actions and their corresponding equivalence classes are closely related to combinatorial problems arising in the context of Coxeter groups, sequential dynamical systems, the chip-firing game, and representations of quivers.
In this paper we construct the graphs C(Y ) and D(Y ) with vertex sets Acyc(Y ) and whose connected components encode the equivalence classes. The number of connected components …