# Events

## August 2019

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### Number Theory Seminar

Thursday, August 1, 2019 — 3:30 PM EDT

“Apollonian packings and Enriques surfaces”

### PhD Thesis Defense

Friday, August 2, 2019 — 10:30 to 10:30 AM EDT

Diana Castaneda Santos, Department of Pure Mathematics, University of Waterloo

"Rational approximations on smooth rational surfaces"

### Geometry Working Seminar

Tuesday, August 6, 2019 — 9:30 AM EDT

Speaker 1: Spencer Whitehead, Department of Pure Mathematics, University of Waterloo

"Regular polytopes and uniform polytopes"

### Algebra Seminar

Tuesday, August 6, 2019 — 2:30 PM EDT

Abdullahi Umar, Khalifa University of Science and Technology, Abu Dhabi, UAE

''Some Remarks on Monoids of Contraction Mappings of a Finite Chain"

### Computability Learning Seminar

Thursday, August 8, 2019 — 10:00 to 10:00 AM EDT

Luke MacLean, Department of Pure Mathematics, University of Waterloo

"Effectively defining formulas in Robinson's Arithmetic"

It was proven by Alfred Tarski that all general recursive functions are definable in Robinson's Arithmetic. I will give his proof of this fact with supplementary information on how to make the process of finding the defining formula effective.

MC 5479

### Valuative Tree Seminar

Monday, August 12, 2019 — 1:00 PM EDT

Ehsaan Hossain, Department of Pure Mathematics, University of Waterloo

"Fixed point theorem for trees"

Brett and Matt talked about $V_0$ and $V_\infty$, two different subtrees of the Berkovich plane. All of these are rooted trees. I will either talk about potential theory on trees, or the theorem that every tree map admits a fixed point.

MC 5403

### Computability Learning Seminar

Thursday, August 15, 2019 — 10:00 to 10:00 AM EDT

Michael Deveau, Department of Pure Mathematics, University of Waterloo

"Computability of Walker's Cancellation Theorem"

### August 2019

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