## Mathematics## Seminar |

## Rocky Mountain Algebraic Combinatorics Seminar

### Unravelling Primitivity

Alexander Hulpke

CSU

Every 2-transitive group is primitive, but not every primitive group is 2-transitive. Recent combinatorial definitions allow for a better analysis of the area between these two definitions. I will look at some of these definitions and consider ways how to test for them. This is joint work with Peter Cameron and Joao Araujo.

### Graph Labelings and Computability Theory

Oscar Levin

University of Northern Colorado

A graph labeling assigns integers to vertices, edges, or both, subject to certain conditions. For example, a labeling is graceful if the difference of labels on adjacent vertices is distinct for all edges, while a labeling is edge-magic if the sum of the labels on an edge and its incident vertices is constant for all edges. Graph labelings are usually studied for finite graphs, but some work has been done to extend these to infinite cases. In this talk we will consider the computable analogues to some results for graceful, edge-magic, and related labelings of infinite graphs. Using ideas from computability theory, we will explore the connection between the complexity of a graph's presentation and the complexity of its labelings. We will share a few initial findings and many directions for future research.

Weber 223

4–6 pm

Friday, September 30, 2016

(Refreshments in Weber 117, 3:30–4 pm)

Colorado State University

This is a joint Denver U / UC Boulder / UC Denver / U of Wyoming / CSU seminar that meets biweekly. Anyone interested is welcome to join us at a local restaurant for dinner after the talks.