# Symmetric, pseudo-symmetric, and almost-symmetric numerical semigroups

## Date:

Wednesday, 15 February, 2012 - 14:30

## Venue:

Room M007 of the Mathematics Department, FCUP

A numerical semigroup $S$ is a submonoid of $(\mathbb N,+)$ with finite complement in $\mathbb N$. Integers not in $S$ are called gaps of $S$. The largest gap is known as the Frobenius number of $S$, $F(S)$. A gap $x$ is a hole, if $F(S)-x$ is also a gap.
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# Coclass theory for nilpotent semigroups

## Speaker:

Andreas Distler (CAUL)

## Date:

Wednesday, 8 February, 2012 - 14:30

## Venue:

Sala 0.04 - Dep. Matemática / FCUP

Coclass theory has been a highly successful approach towards the investigation and classification of finite nilpotent groups. In joint work with Bettina Eick I investigate a similar approach for the study of finite nilpotent semigroups.
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# Verification Conditions for Single-assignment Programs

## Speaker:

Jorge Sousa Pinto (Departamento de Informática, Escola de Engenharia, Universidade do Minho

## Date:

Wednesday, 30 November, 2011 (All day)

## Venue:

S2, DCC-FCUP

A mechanism for generating verification conditions (VCs) for the iteration-free fragment of an imperative language is fundamental in any deductive program verification system. In this paper we revisit symbolic execution, weakest preconditions, and bounded model checking as VC-generation...

# Amalgams of inverse semigroups and reversible two-counter machines

## Speaker:

Emanuele Rodaro (CMUP)

## Date:

Wednesday, 23 November, 2011 - 14:30

## Venue:

Sala 0.04 - Dep. Matemática / FCUP

(Join work with Pedro Silva) We show that the word problem for an amalgam [S1, S2; U, ω1, ω2] of inverse semigroups may be undecidable even if we assume S1 and S2 (and therefore U) to have finite R-classes and ω1, ω2 to be computable functions, interrupting a series of...

# Computing generalised Feng-Rao numbers of numerical semigroups

## Date:

Wednesday, 26 October, 2011 - 13:30

## Venue:

Sala 0.04 - Dep. Matemática / FCUP

A numerical semigroup is a co-finite submonoid of the non-negative integers under addition
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# Finite automata for Schreier graphs of virtually free groups

## Speaker:

Pedro V. Silva (FCUP / CMUP)

## Date:

Wednesday, 21 September, 2011 - 13:30

## Venue:

Sala 0.04 - Dep. Matemática / FCUP

# A categorical invariant of flow equivalence.

## Speaker:

Alfredo Costa (FCTUC/CMUC)

## Date:

Monday, 31 January, 2011 - 14:30

## Venue:

Sala 0.04 – Dep. Matemática/FCUP

The Karoubi envelope of a semigroup is a small category which plays a distinguished role in finite semigroup theory thanks to the Delay theorem of Tilson. In this talk, an application to the classification of symbolic dynamical systems is presented: up to natural equivalence, the Karoubi envelope...