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Taking a Feynman categorical perspective, several key aspects of the geometry of surfaces are deduced from combinatorial constructions with graphs. This provides a direct route from combinatorics of graphs to string topology operations via…

Algebraic Topology · Mathematics 2022-01-26 Clemens Berger , Ralph M. Kaufmann

In this paper, we introduce a new approach for drawing diagrams that have applications in software visualization. Our approach is to use a technique we call confluent drawing for visualizing non-planar diagrams in a planar way. This…

Computational Geometry · Computer Science 2007-05-23 Matthew Dickerson , David Eppstein , Michael T. Goodrich , Jeremy Meng

Abstract inner automorphisms can be used to promote any category into a 2-category, and we study two-dimensional limits and colimits in the resulting 2-categories. Existing connected colimits and limits in the starting category become…

Category Theory · Mathematics 2025-09-08 Pieter Hofstra , Martti Karvonen

A graph is rectilinear planar if it admits a planar orthogonal drawing without bends. While testing rectilinear planarity is NP-hard in general (Garg and Tamassia, 2001), it is a long-standing open problem to establish a tight upper bound…

Data Structures and Algorithms · Computer Science 2023-06-23 Walter Didimo , Michael Kaufmann , Giuseppe Liotta , Giacomo Ortali

We investigate the problem of drawing graphs in 2D and 3D such that their edges (or only their vertices) can be covered by few lines or planes. We insist on straight-line edges and crossing-free drawings. This problem has many connections…

Computational Geometry · Computer Science 2016-09-02 Steven Chaplick , Krzysztof Fleszar , Fabian Lipp , Alexander Ravsky , Oleg Verbitsky , Alexander Wolff

We study lax functors between bicategories as a generalized concept of monads and describe generalized notions and theorems of formal monad theory for lax functors. Our first approach is to use the 2-monad whose lax algebras are lax…

Category Theory · Mathematics 2024-09-20 Kengo Hirata

Categorification is the process of finding category-theoretic analogs of set-theoretic concepts by replacing sets with categories, functions with functors, and equations between functions by natural isomorphisms between functors, which in…

Quantum Algebra · Mathematics 2014-11-18 John C. Baez , James Dolan

Category theory has foundational importance because it provides conceptual lenses to characterize what is important in mathematics. Originally the main lenses were universal mapping properties and natural transformations. In recent decades,…

Category Theory · Mathematics 2007-05-23 David Ellerman

A 2-group is a `categorified' version of a group, in which the underlying set G has been replaced by a category and the multiplication map m: G x G -> G has been replaced by a functor. A number of precise definitions of this notion have…

Category Theory · Mathematics 2007-05-23 Aaron D. Lauda

A digraph is 2-regular if every vertex has both indegree and outdegree two. We define an embedding of a 2-regular digraph to be a 2-cell embedding of the underlying graph in a closed surface with the added property that for every…

Combinatorics · Mathematics 2017-06-12 Dan Archdeacon , Matt DeVos , Stefan Hannie , Bojan Mohar

In this paper we study graphs which admit acyclic orientations that contain a pair of arc-disjoint out-branching and in-branching (such an orientation is called good) and we focus on edge-minimal such graphs. A 2T-graph is a graph whose…

Combinatorics · Mathematics 2019-03-26 J. Bang-Jensen , S. Bessy , J. Huang , M. Kriesell

In a closed 2-cell embedding of a graph each face is homeomorphic to an open disk and is bounded by a cycle in the graph. The Orientable Strong Embedding Conjecture says that every 2-connected graph has a closed 2-cell embedding in some…

Combinatorics · Mathematics 2009-11-17 M. N. Ellingham , Xiaoya Zha

In some bicategories, the 1-cells are `morphisms' between the 0-cells, such as functors between categories, but in others they are `objects' over the 0-cells, such as bimodules, spans, distributors, or parametrized spectra. Many…

Category Theory · Mathematics 2010-03-15 Michael A. Shulman

Generalizing the classical matrix-tree theorem we provide a formula counting subgraphs of a given graph with a fixed 2-core. We use this generalization to obtain an analog of the matrix-tree theorem for the root system $D_n$ (the classical…

Combinatorics · Mathematics 2007-05-23 Yurii Burman , Boris Shapiro

Comparability graphs are a popular class of graphs. We introduce as the digraph analogue of comparability graphs the class of comparability digraphs. We show that many concepts such as implication classes and the knotting graph for a…

Combinatorics · Mathematics 2022-04-05 Xiao-Lu Gao , Jing Huang , Shou-Jun Xu

Bispanning graphs are undirected graphs with an edge set that can be decomposed into two disjoint spanning trees. The operation of symmetrically swapping two edges between the trees, such that the result is a different pair of disjoint…

Combinatorics · Mathematics 2016-05-12 Timo Bingmann

We introduce polytopal cell complexes associated with partial acyclic orientations of a simple graph, which generalize acyclic orientations. Using the theory of cellular resolutions, two of these polytopal cell complexes are observed to…

Combinatorics · Mathematics 2015-02-10 Benjamin Iriarte Giraldo

A theory of sketches for arithmetic universes (AUs) is developed. A restricted notion of sketch, called here "context", is defined with the property that every non-strict model is uniquely isomorphic to a strict model. This allows us to…

Category Theory · Mathematics 2016-08-05 Steven Vickers

Beyond-planarity focuses on the study of geometric and topological graphs that are in some sense nearly-planar. Here, planarity is relaxed by allowing edge crossings, but only with respect to some local forbidden crossing configurations.…

Discrete Mathematics · Computer Science 2017-12-29 Patrizio Angelini , Michael A. Bekos , Michael Kaufmann , Maximilian Pfister , Torsten Ueckerdt

The primary goal of this paper is to abstract notions, results and constructions from the theory of categories to the broader setting of plots. Loosely speaking, a plot can be thought of as a non-associative non-unital category with a…

Category Theory · Mathematics 2016-04-06 Salvatore Tringali