
Please note that schedules are subject to change without notice, particularly changes within a given session.
Algebraic graph theory in quantum computing  
Org: Ada Chan (York University)  
Quantum walks are an important concept in the study of quantum algorithms. Quantum walk algorithms have been studied and shown to perform exponentially or polynomially better for various black box problems. Problems about quantum walks on graphs have also produced numerous interesting mathematical problems, where techniques in algebraic graph theory have yielded new advances. This minisymposium will give an overview of recent work along this vein, as well as encourage further collaboration.
Other organizers: Chris Godsil (University of Waterloo), Krystal Guo (University of Waterloo), and Christino Tamon (Clarkson University)  
Thursday June 15  
15:20  15:45  Luc Vinet (University of Montreal), NEXTTONEAREST NEIGHBOUR COUPLINGS AND ENTANGLEMENT GENERATION IN SPIN CHAINS AND OPTICAL ARRAYS 
15:50  16:15  Christopher van Bommel (University of Waterloo), Characterizing Pretty Good State Transfer on Paths 
16:20  16:45  Mark Kempton (Harvard University), Quantum state transfer on graphs 
16:50  17:15  Thomas Wong (University of Texas at Austin), Degenerate Perturbation Theory as a Tool for Quantum Search 
17:20  17:45  Harmony Zhan (University of Waterloo), DiscreteTime Quantum Walks and Graph Structures 
Average Graph Parameters I  
Org: Ortrud Oellermann and Lucas Mol (University of Winnipeg)  
Probably the oldest and most wellknown average graph parameter, the average distance of a graph  also known as the Wiener index, dates back to 1947. Of particular interest is the close correlation of the Wiener index of the molecular graph and the chemical properties of the substance such as the boiling point, viscosity and surface tension. In this minisymposium results on various average graph parameters such as the average distance in a digraph, the average order of subtrees of trees and some of its generalizations, as well as the average reliability of a graph and their relationships with the structural properties of the (di)graph are presented.  
Monday June 12  
15:20  15:45  Danielle Cox (Mount Saint Vincent University), The Average Reliability of a Graph 
15:50  16:15  Peter Dankelmann (University of Johannesburg), Bounds on the average distance of directed graphs 
16:20  16:45  Lucas Mol (University of Winnipeg), Maximizing mean subtree order for classes of trees 
16:50  17:15  Ortrud Oellermann (University of Winnipeg), On the mean order of sub$k$trees of $k$trees 
17:20  17:45  Hua Wang (Georgia Southern University), On the average subtree order of trees and related studies 
Combinatorial Gray codes  
Org: Jan Goedgebeur (Ghent University) and Torsten MÃ¼tze (TU Berlin)  
Generating all the objects in a particular class (e.g. permutations, subsets, strings, trees, graphs etc.) such that each object is generated exactly once is one of the oldest and most basic combinatorial problems, with a large number of practical applications. In fact, more than half of Donald Knuth's most recent book in the seminal series 'The Art of Computer Programming' is entirely devoted to this fundamental subject. This minisymposium aims at presenting some of the exciting recent developments in the area of combinatorial Gray codes, and to circulate challenging open problems among researchers in the field. This minisymposium has a companion entitled `Computational combinatorics' in which such generation algorithms have been applied successfully to solve various combinatorial problems.  
Monday June 12  
10:20  10:45  Aaron Williams (Bard College at Simon's Rock), The Twelvefold Way with Greedy Gray Codes 
10:50  11:15  Dennis Wong (Northwest Missouri State University), Induced 2Gray codes inside the Binary Reflected Gray Code 
11:20  11:45  Joe Sawada (University of Guelph), New and simple de Bruijn sequence constructions 
11:50  12:15  Torsten MÃ¼tze (TU Berlin), Trimming and gluing Gray codes 
Combinatorial Optimization  
Org: Guyslain Naves (AixMarseille University) and Bruce Shepherd (McGill)  
Minmax results (exact and approximate) and new models in combinatorial optimization arising from flows, cuts, and matroids.  
Monday June 12  
15:20  15:45  Ahmad Abdi (Waterloo), Ideal clutters that do not pack 
15:50  16:15  Andras Frank (Eotvos Lorand University), Finding $k$ disjoint branchings with specified sizes 
16:20  16:45  Vivek Madan (Uuniversity Illininois UrbanaChampaign), Revisiting Cut problems and Labelling LPs 
16:50  17:15  Richard Santiago (McGill University), Multiagent Submodular Optimization 
17:20  17:45  Bruce Shepherd (McGill University), ConflictFree Disjoint Paths and Stable Matchings 
Computational combinatorics  
Org: Jan Goedgebeur (Ghent University) and Torsten MÃ¼tze (TU Berlin)  
Computers are often used in combinatorics to determine if combinatorial objects with given structural or extremal properties exist as these existence problems are often too complex to solve by hand. This is done by designing and implementing generation algorithms which construct combinatorial objects from a given class (typically avoiding the generation of isomorphic copies).
This minisymposium presents some recent examples where computers have been successfully used to solve problems in graph colouring, Hamiltonicity and Ramsey theory. This minisymposium has a companion entitled `Combinatorial Gray codes', covering algorithms for generating various families of combinatorial objects, which are an essential tool for such exhaustive enumeration approaches.  
Tuesday June 13  
15:20  15:45  Richard Brewster (Thompson Rivers University), Computational examples for aiding graph theory research 
15:50  16:15  Jan Goedgebeur (Ghent University), Generation of hypohamiltonian graphs 
16:20  16:45  Gary MacGillivray (University of Victoria), Hamiltonicity of Bell and Stirling colour graphs 
16:50  17:15  Stanislaw Radziszowski (Rochester Institute of Technology), Chromatic vertex Folkman numbers, general Folkman problems, and related computational challenges 
Discrete Mathematical Biology, Part I  
Org: Torin Greenwood and Christine Heitsch (Georgia Institute of Technology)  
This pair of minisymposia will examine discrete models and combinatorial methods across a spectrum of mathematical biology. Problems in biology motivate new combinatorial methods, which have intrinsic mathematical appeal. Complementing this, new mathematical techniques bring advancements to biology. These talks exhibit the fruitful interplay between the fields.  
Tuesday June 13  
10:20  10:45  Sharlee Climer (University of Missouri  St. Louis), Embracing the complexity of combinatorial GWAS 
10:50  11:15  Joanna EllisMonaghan (Saint Michael's College), Ins and Outs of DNA SelfAssembly 
11:20  11:45  Torin Greenwood (Georgia Institute of Technology), Using Experimental Data to Deconvolve Structural Signals 
11:50  12:15  Ezra Miller (Duke University), Fruit fly wing veins as embedded planar graphs 
12:20  12:45  Sonja Petrovic (Illinois Institute of Technology), Discrete methods for statistical network analysis in biology 
Discrete Mathematical Biology, Part II  
Org: Torin Greenwood and Christine Heitsch (Georgia Institute of Technology)  
This pair of minisymposia will examine discrete models and combinatorial methods across a spectrum of mathematical biology. Problems in biology motivate new combinatorial methods, which have intrinsic mathematical appeal. Complementing this, new mathematical techniques bring advancements to biology. These talks exhibit the fruitful interplay between the fields.  
Tuesday June 13  
15:20  15:45  Peter Clote (Boston College), Network properties of RNA secondary structures 
15:50  16:15  Elena Dimitrova (Clemson University), Unique Reduced Gr\"obner Bases of Ideals of Points 
16:20  16:45  Tara Petrie (Simon Fraser University), Folding something other than laundry 
16:50  17:15  Christian Reidys (Virginia Institute of Technology), a new grammar for PKstructures 
17:20  17:45  David Sivakoff (Ohio State University), Discrete Excitable Media 
Entropy compression and the Lovasz Local Lemma  
Org: Michael Molloy (University of Toronto)  
The Lovasz Local Lemma is a powerful proof technique which proves the existence of an object, by showing that a random procedure attempting to produce it will succeed with positive probability. For example, every graph with certain properties has a colouring of a certain type.
$\\$
In 2008, Moser introduced entropy compression, a technique to provide efficient algorithms which construct objects that the Local Lemma guarantees to exist. His technique has since been used to obtain new existence proofs using procedures where it is hard to apply traditional versions of the Local Lemma. For example, one can try to colour a graph by colouring vertices oneatatime, each time choosing a random colour that does not appear on the neighbourhood of the vertex. The spread of dependencies in such a procedure is usually too much for the Local Lemma. But procedures of this type can fit quite well into Moser's framework.  
Wednesday June 14  
10:20  10:45  Fotis Iliopoulos (UC Berkeley), Stochastic Local Search and the Lovasz Local Lemma 
10:50  11:15  Gwenael Joret (UniversitÃ© Libre de Bruxelles), Improved bound for AVD edge coloring 
11:20  11:45  Piotr Micek (Jagiellonian University), Nonrepetitive colorings and entropy compression method 
11:50  12:15  Michael Molloy (University of Toronto), Colouring graphs with small clique number 
Geometry and Combinatorial Optimization  
Org: Guyslain Naves (AixMarseille University)  
This session's focus is on geometric aspects of combinatorial optimization.  
Tuesday June 13  
15:20  15:45  Marcel Celaya (Georgia Tech), The linear span of lattice points in the halfopen unit cube 
15:50  16:15  Robert Davis (Michigan State University), Detecting the Integer Decomposition Property in Reflexive Simplices 
16:20  16:45  Guyslain Naves (Marseille University), Packing and covering with balls on Busemann surfaces 
16:50  17:15  Andras Sebo (Grenoble), Tours, Colouring or Somewhere In Between 
17:20  17:45  Nicholas Early (Penn State), How to Scale A Hypersimplex 
Graph Colouring, Part I  
Org: Luke Postle (University of Waterloo)  
Graph coloring is one the oldest and most storied areas of graph theory. Despite dating back to the days of the Four Color Conjecture, there has been much recent interest and active progress in this area, especially in the last few decades. Many generalizations of graph coloring, developed to tackle practical problems, can be extended beyond their original applications in order to attack new areas. This twopart minisymposium seeks to highlight a number of these interesting new developments by bringing together researchers in this classical field.  
Monday June 12  
15:20  15:45  Michelle Delcourt (University of Illinois at UrbanaChampaign), On the List Coloring Version of Reed's Conjecture 
15:50  16:15  Thomas Kelly (University of Waterloo), Beyond DegreeChoosability Toward a Local Epsilon Version of Reed's $\omega, \Delta, \chi$ conjecture 
16:20  16:45  Sophie Spirkl (Princeton University), Even Pairs and Prism Corners in Perfect Graphs 
16:50  17:15  David Wood (Monash University), Defective colouring of graphs excluding a subgraph or minor 
17:20  17:45  Hehui Wu (Shanghai Center for Mathematical Sciences), Digraphs coloring and tournaments with large domination number 
Graph Colouring, Part II  
Org: Michelle Delcourt (University of Illinois at UrbanaChampaign)  
Graph coloring is one the oldest and most storied areas of graph theory. Despite dating back to the days of the Four Color Conjecture, there has been much recent interest and active progress in this area, especially in the last few decades. Many generalizations of graph coloring, developed to tackle practical problems, can be extended beyond their original applications in order to attack new areas. This twopart minisymposium seeks to highlight a number of these interesting new developments by bringing together researchers in this classical field.  
Tuesday June 13  
10:20  10:45  Anton Bernshteyn (University of Illinois at UrbanaChampaign), Dirac's theorem for DPcritical graphs 
10:50  11:15  Vida Dujmovic (University of Ottawa), Layered treecompositions and graph colouring 
11:20  11:45  Felix Joos (University of Birmingham), The Tree Packing Conjecture 
11:50  12:15  Luke Postle (University of Waterloo), List Coloring with Requests 
12:20  12:45  Yelena Yuditsky (McGill University), Gy\'arf\'asSumner Conjecture Is Almost Always True 
Graph Polynomials  
Org: Jason Brown (Dalhousie University)  
For a variety of combinatorial problems, such as network reliability and graph colourings, the models turn out to be graph polynomials. On the other hand, the investigation of various subgraph properties (such as independence and domination) leads one to explore the associated combinatorial sequences by formulating generating polynomials. In all cases, polynomials carry useful or even essential information about the underlying combinatorics, and the connections allow one to draw on classical areas of mathematics, such as analysis and algebra, in the investigations.  
Tuesday June 13  
15:20  15:45  Jason Brown (Dalhousie University), Recent Results on Chromatic Polynomials 
15:50  16:15  Ben Cameron (Dalhousie University), On the Unimodality of Independence Polynomials of Very WellCovered Graphs 
16:20  16:45  Danielle Cox (Mount Saint Vincent University), Analytic Properties of the Reliability Polynomial 
16:50  17:15  Lucas Mol (University of Winnipeg), Roots of allterminal reliability and node reliability polynomials 
17:20  17:45  David Wagner (University of Waterloo), The algebra of flows in graphs 
Graph Structure and Algorithms I  
Org: Kathie Cameron and Shenwei Huang (Wilfrid Laurier University / University of New South Wales)  
Graph algorithms are at the core of discrete mathematics and computer science. They play an increasingly critical role in fundamental research as well as real applications. In this minisymposium, we will hear a variety of exciting developments on classical and parameterized complexity of graph problems such as coloring, homomorphisms and graph search, and on structure of important classes of graphs and digraphs.  
Wednesday June 14  
10:20  10:45  CÃ©sar HernÃ¡ndez Cruz (Universidad Nacional AutÃ³noma de MÃ©xico), Cograph minimal $(s,k)$polar obstructions. 
10:50  11:15  Edward Lee (University of New South Wales), Fast exponentialtime algorithms via multivariate subroutines 
11:20  11:45  Jing Huang (University of Victoria), Endvertices of lexicographic breadth first searches 
11:50  12:15  Shenwei Huang (University of New South Wales), Linearly $\chi$Bounding $(P_6,C_4)$Free Graphs 
12:20  12:45  Arash Rafiey (Indiana State University), Biarc Digraphs and Conservative Polymorphisms 
Graph Structure and Algorithms II  
Org: Kathie Cameron and Shenwei Huang (Wilfrid Laurier University / University of New South Wales)  
Graph algorithms are at the core of discrete mathematics and computer science. They play an increasingly critical role in fundamental research as well as real applications. In this minisymposium, we will hear a variety of exciting developments on classical and parameterized complexity of graph problems such as coloring, homomorphisms and graph search, and on structure of important classes of graphs and digraphs.  
Wednesday June 14  
15:20  15:45  Kathie Cameron (Wilfrid Laurier University), Solving the clique cover problem on (bull, $C_4$)free graphs 
15:50  16:15  Elaine Eschen (West Virginia University), Colored graph completion problem for classes of chordal graphs 
16:20  16:45  Pavol Hell (Simon Fraser University), Digraph Analogues of Nice Graph Classes 
16:50  17:15  Chinh Hoang (Wilfrid Laurier University), Coloring graphs without small forbidden subgraphs 
17:20  17:45  R. Sritharan (University of Dayton), Graph modification problem 
Graphs and Games: the Mathematics of Richard Nowakowski (Part I)  
Org: Shannon Fitzpatrick (University of Prince Edward Island)  
This minisymposium is in honour of Richard Nowakowski, on the occasion of his 65th birthday. Throughout his career, Richard has worked on a variety of problems, but his influence has been most keenly felt in the fields of Graph Searching and Combinatorial Game Theory. This is an opportunity for Richard's former students, collaborators, and colleagues to present research in areas of particular interest to Richard, and celebrate his contribution to mathematics in Canada.  
Tuesday June 13  
10:20  10:45  Nancy Clarke (Acadia University), Cops and Robbers with Gangs 
10:50  11:15  Stephen Finbow (Saint Francis Xavier University), Eternal Domination Game on King Graphs 
11:20  11:45  Shannon Fitzpatrick (University of Prince Edward Island), The Game of kVisibility Cops and Robber 
11:50  12:15  Neil McKay (University of New Brunswick, Saint John), Brussels Sprouts, Lattices, and Game Trees 
12:20  12:45  MargaretEllen Messinger (Mount Allison University), Chip Diffusion 
Graphs and Games: the Mathematics of Richard Nowakowski (Part II)  
Org: MargaretEllen Messinger (Mount Allison University)  
This minisymposium is in honour of Richard Nowakowski, on the occasion of his 65th birthday. Throughout his career, Richard has worked on a variety of problems, but his influence has been most keenly felt in the fields of Graph Searching and Combinatorial Game Theory. This is an opportunity for Richard's former students, collaborators, and colleagues to present research in areas of particular interest to Richard, and celebrate his contribution to mathematics in Canada.  
Wednesday June 14  
10:20  10:45  Anthony Bonato (Ryerson University), Games and graphs: the legacy of RJN 
10:50  11:15  Jason Brown (Dalhousie University), My Streak of Independence with Richard 
11:20  11:45  Chris Duffy (Dalhousie University), Shapleyâ€“Shubik Power Index as a Model for Spread of Influence in a Network 
11:50  12:15  Gena Hahn (UniversitÃ© de MontrÃ©al), Loops or no loops? 
12:20  12:45  Pawel Pralat (Ryerson University), A probabilistic version of the game of Zombies and Survivors on graphs 
Graphs and Games: the Mathematics of Richard Nowakowski (Part III)  
Org: Nancy Clarke (Acadia University)  
This minisymposium is in honour of Richard Nowakowski, on the occasion of his 65th birthday. Throughout his career, Richard has worked on a variety of problems, but his influence has been most keenly felt in the fields of Graph Searching and Combinatorial Game Theory. This is an opportunity for Richard's former students, collaborators, and colleagues to present research in areas of particular interest to Richard, and celebrate his contribution to mathematics in Canada.  
Wednesday June 14  
15:20  15:45  Art Finbow (Saint Mary's University), Extendable Vertices in WellCovered Graphs 
15:50  16:15  Bert Hartnell (Saint Mary's University), Parity Dissociation Graphs 
16:20  16:45  Jeannette Janssen (Dalhousie University), An application of Hall's theorem to linear embeddings of graphs 
16:50  17:15  Mike Plummer (Vanderbilt University), 4regular planar wellcovered graphs 
In honour of the work of Alex Rosa (Part I)  
Org: Peter Danziger, Tommaso Traetta (Ryerson University)  
On the occasion of Alex Rosa's 80th birthday we offer these two sessions in honour of his work. Particularly known for his work on Triple Sytems, Dr. Rosa has published in many areas of Combinatorics including Graph Labellings, Steiner Triple systems and Graph Decompositions. He has over 200 refereed journal publications, many books, and was a founding editor of the Journal of Combinatorial Designs. He has been awarded the prestigous Euler medal by the Institute of Combinatorics and its Applications. He is universally recognised as one of the leading lights of modern Combinatorics, his activities and influence in Discrete Mathematics continue to this day. These sessions will highlight recent progress in areas of interest in Design Theory and beyond to which Alex has blazed the trail.  
Tuesday June 13  
10:20  10:45  Peter Dukes (University of Victoria), Fractional decompositions and completing partial latin squares 
10:50  11:15  FranÄ›k FrantiÅ¡ek (McMaster University), dstep approach to periodical structures in strings 
11:20  11:45  Esther Lamken (University of Caltech), An existence theory for incomplete designs 
11:50  12:15  Nabil Shalaby (Memorial University), Rosa sequences 
12:20  12:45  Doug Stinson (University of Waterloo), Some results on the existence of tallornothing transforms over arbitrary alphabets 
In honour of the work of Alex Rosa (Part II)  
Org: Peter Danziger, Tommaso Traetta (Ryerson University)  
On the occasion of Alex Rosa's 80th birthday we offer these two sessions in honour of his work. Particularly known for his work on Triple Systems, Dr. Rosa has published in many areas of Combinatorics including Graph Labellings, Steiner Triple systems and Graph Decompositions. He has over 200 refereed journal publications, many books, and was a founding editor of the Journal of Combinatorial Designs. He has been awarded the prestigious Euler medal by the Institute of Combinatorics and its Applications. He is universally recognised as one of the leading lights of modern Combinatorics, his activities and influence in Discrete Mathematics continue to this day. These sessions will highlight recent progress in areas of interest in Design Theory and beyond to which Alex has blazed the trail.  
Tuesday June 13  
15:20  15:45  Andrea Burgess (University of New Brunswick), Recent advances on the HamiltonWaterloo problem 
15:50  16:15  Barbara Maenhaut (University of Queensland), Hamilton Decompositions of Line Graphs 
16:20  16:45  David Pike (Memorial University), Colourings of Group Divisible Designs 
16:50  17:15  Brett Stevens (Carleton University), KirkmanHamilton triple systems 
17:20  17:45  Tommaso Traetta (Ryerson University), Reverse $2$factorizations via graceful labelings 
PursuitEvasion Games on Graphs  
Org: Bill Kinnersley (University of Rhode Island)  
Pursuitevasion games are a type of combinatorial game in which one or more ``pursuers'' attempts to capture a mobile ``evader'' within some environment (often represented by a graph). In addition to being of theoretical interest, pursuitevasion games have applications in a variety of areas, from mobile computing to military operations. This minisymposium will focus on recent developments in the field, with a particular emphasis on the classic game of Cops and Robbers.  
Monday June 12  
15:20  15:45  Danny Dyer (Memorial University), Watching Halin graphs 
15:50  16:15  Saeed Aliasghar Hosseini (Simon Fraser University), Cops and Robbers on Oriented Grids 
16:20  16:45  Bill Kinnersley (University of Rhode Island), Bounds on the Capture Time of Graphs 
16:50  17:15  Natasha Komarov (St. Lawrence University), Using spotlights to find a robber 
17:20  17:45  Kerry Ojakian (Bronx Community College (C.U.N.Y.)), Extremal CopWin Graphs 
Reconfiguration  
Org: Ruth Haas (U. Hawaii, Manoa)  
The reconfiguration version of a problem concerns when one feasible solution to a problem can be reconfigured to another via an allowable set of operations. There has recently been a lot of interest in this topic including reconfiguration of graph coloring and domination among other problems These talks give an overview of the area as well as current work and open problems.  
Wednesday June 14  
15:20  15:45  Naomi Nishimura (Waterloo), Introduction to Reconfiguration 
15:50  16:15  Benjamin Moore (Simon Fraser University), Some observations on circular colouring mixing for $(p,q)$colourings when $p/q <4$ 
16:20  16:45  Karen Seyffarth (U Calgary), Reconfiguring Vertex Colourings of 2trees 
16:50  17:15  Moritz MÃ¼hlenthaler (ErlangenNurnberg), Reconfiguration of Common Independent Sets of Partition Matroids 
17:20  17:45  Beth Novick (Clemson University), Structural Properties of Shortest Path Graphs 
Topological and Geometric Algorithms, Part I  
Org: Mark Ellingham and Joanna EllisMonaghan (Vanderbilt University and Saint Michael's College)  
One of the strengths of discrete mathematics is its broad applicability in a wide range of other fields. For example, many problems in discrete mathematics have a topological or geometric component or setting. Moreover, particularly for questions driven by applications, many such problems include algorithmic approaches. This minisymposium brings together researchers whose work in discrete mathematics involves both spatial and computational considerations, many with a subtheme of structural questions arising from biological and other applications. Examples include: graph drawing in various settings; determining folding configurations for paper, DNA, or protein structures; and generating graph embeddings with certain symmetries.  
Monday June 12  
10:20  10:45  Ileana Streinu (Smith College), Rigidity and flexibility in molecular graphs: the KINARI experience 
10:50  11:15  Ciprian Borcea (Rider University), Periodic frameworks: graphs, placements, deformations 
11:20  11:45  Christine Heitsch (Georgia Institute of Technology), Meanders and RNA Folding 
11:50  12:15  NataÅ¡a Jonoska (University of South Florida), Topological graph theory in DNA selfassembly and DNA recombination 
12:20  12:45  Ada Morse (University of Vermont), DNA Origami and Knots in Graphs 
Topological and Geometric Algorithms, Part II  
Org: Mark Ellingham and Joanna EllisMonaghan (Vanderbilt University and Saint Michael's College)  
One of the strengths of discrete mathematics is its broad applicability in a wide range of other fields. For example, many problems in discrete mathematics have a topological or geometric component or setting. Moreover, particularly for questions driven by applications, many such problems include algorithmic approaches. This minisymposium brings together researchers whose work in discrete mathematics involves both spatial and computational considerations, many with a subtheme of structural questions arising from biological and other applications. Examples include: graph drawing in various settings; determining folding configurations for paper, DNA, or protein structures; and generating graph embeddings with certain symmetries.  
Thursday June 15  
10:20  10:45  Mark Ellingham (Vanderbilt University), Graph embeddings and DNA reporter strands 
10:50  11:15  Ellen Gethner (University of Colorado Denver), Thickness, Simultaneous Embeddings, and Graph Sculpting 
11:20  11:45  Anna Lubiw (University of Waterloo), Flipping EdgeLabelled Triangulations 
11:50  12:15  Therese Biedl (University of Waterloo), Optimumwidth upward drawings of trees 
12:20  12:45  Sue Whitesides (University of Victoria), Visibility Graphs: a survey 