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A graph on $n \ge 3$ vertices drawn in the plane such that each edge is crossed at most four times has at most $6(n-2)$ edges -- this result proven by Ackerman is outstanding in the literature of beyond-planar graphs with regard to its…

Combinatorics · Mathematics 2025-10-03 Aaron Büngener

A graph is \emph{fan-crossing free} if it has a drawing in the plane so that each edge is crossed by independent edges, that is the crossing edges have distinct vertices. On the other hand, it is \emph{fan-crossing} if the crossing edges…

Discrete Mathematics · Computer Science 2020-12-14 Franz J. Brandenburg

For a planar graph with a given f-vector $(f_{0}, f_{1}, f_{2}),$ we introduce a cubic polynomial whose coefficients depend on the f-vector. The planar graph is said to be real if all the roots of the corresponding polynomial are real. Thus…

Combinatorics · Mathematics 2018-03-29 M. R. Emamy-K. , Bahman Kalantari , Tatiana Correa

A graph is 1-planar if it has a drawing where each edge is crossed at most once. A drawing is RAC (Right Angle Crossing) if the edges cross only at right angles. The relationships between 1-planar graphs and RAC drawings have been partially…

Computational Geometry · Computer Science 2016-08-31 Walter Didimo , Giuseppe Liotta , Saeed Mehrabi , Fabrizio Montecchiani

The 2-blowup of a graph is obtained by replacing each vertex with two non-adjacent copies; a graph is biplanar if it is the union of two planar graphs. We disprove a conjecture of Gethner that 2-blowups of planar graphs are biplanar:…

Combinatorics · Mathematics 2024-10-29 David Eppstein

A topological graph is a graph drawn in the plane. A topological graph is $k$-plane, $k>0$, if each edge is crossed at most $k$ times. We study the problem of partitioning the edges of a $k$-plane graph such that each partite set forms a…

Simple drawings are drawings of graphs in which any two edges intersect at most once (either at a common endpoint or a proper crossing), and no edge intersects itself. We analyze several characteristics of simple drawings of complete…

Computational Geometry · Computer Science 2023-08-22 Oswin Aichholzer , Birgit Vogtenhuber , Alexandra Weinberger

We study the 1-planar, quasi-planar, and fan-planar crossing number in comparison to the (unrestricted) crossing number of graphs. We prove that there are $n$-vertex 1-planar (quasi-planar, fan-planar) graphs such that any 1-planar…

Computational Geometry · Computer Science 2019-09-10 Markus Chimani , Philipp Kindermann , Fabrizio Montecchiani , Pavel Valtr

Every finite graph admits a \emph{simple (topological) drawing}, that is, a drawing where every pair of edges intersects in at most one point. However, in combination with other restrictions simple drawings do not universally exist. For…

Computational Geometry · Computer Science 2020-08-26 Michael Hoffmann , Chih-Hung Liu , Meghana M. Reddy , Csaba D. Tóth

We prove that in any strongly fan-planar drawing of a graph G the edges can be colored with at most three colors, such that no two edges of the same color cross. This implies that the thickness of strongly fan-planar graphs is at most…

Combinatorics · Mathematics 2022-08-29 Otfried Cheong , Maximilian Pfister , Lena Schlipf

A nearly platonic graph is a k-regular simple planar graph in which all but a small number of the faces have the same degree. We show that it is impossible for a finite graph to have exactly one disparate face, and offer some conjectures,…

Combinatorics · Mathematics 2016-08-02 Dalibor Froncek , William J. Keith , Donald L. Kreher

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

A visibility representation is a classical drawing style of planar graphs. It displays the vertices of a graph as horizontal vertex-segments, and each edge is represented by a vertical edge-segment touching the segments of its end vertices;…

Computational Geometry · Computer Science 2013-08-26 Franz J. Brandenburg

We investigate straight-line drawings of topological graphs that consist of a planar graph plus one edge, also called almost-planar graphs. We present a characterization of such graphs that admit a straight-line drawing. The…

Computational Geometry · Computer Science 2015-07-01 Peter Eades , Seok-Hee Hong , Giuseppe Liotta , Naoki Katoh , Sheung-Hung Poon

We show that any outerplanar graph admits a planar straightline drawing such that the length ratio of the longest to the shortest edges is strictly less than 2. This result is tight in the sense that for any $\epsilon > 0$ there are…

Computational Geometry · Computer Science 2017-09-04 Sylvain Lazard , William Lenhart , Giuseppe Liotta

This paper studies the problem of computing quasi-upward planar drawings of bimodal plane digraphs with minimum curve complexity, i.e., drawings such that the maximum number of bends per edge is minimized. We prove that every bimodal plane…

Computational Geometry · Computer Science 2021-09-14 Carla Binucci , Emilio Di Giacomo , Giuseppe Liotta , Alessandra Tappini

The notion of 1-planarity is among the most natural and most studied generalizations of graph planarity. A graph is 1-planar if it has an embedding where each edge is crossed by at most another edge. The study of 1-planar graphs dates back…

Computational Geometry · Computer Science 2017-07-21 Stephen G. Kobourov , Giuseppe Liotta , Fabrizio Montecchiani

We study geometric and topological properties of infinite graphs that are quasi-isometric to a planar graph of bounded degree. We prove that every locally finite quasi-transitive graph excluding a minor is quasi-isometric to a planar graph…

Combinatorics · Mathematics 2025-06-24 Louis Esperet , Ugo Giocanti

In a planar L-drawing of a directed graph (digraph) each edge e is represented as a polyline composed of a vertical segment starting at the tail of e and a horizontal segment ending at the head of e. Distinct edges may overlap, but not…

Computational Geometry · Computer Science 2020-08-19 Patrizio Angelini , Steven Chaplick , Sabine Cornelsen , Giordano Da Lozzo

We characterise the quintic (i.e. 5-regular) multigraphs with the property that every edge lies in a triangle. Such a graph is either from a set of small graphs or is formed by adding a perfect matching to a line graph of a cubic graph as…

Combinatorics · Mathematics 2021-07-09 James Preen