Category Archives: conferences

2019-08-02

Humuhumunukunukuapua’a at the Symposium

2nd Annual SURE Symposium 2019

SURE: Summer Undergraduate Research Experience

will feature two projects mentored by Prof. Kjos-Hanssen:

VC-dimensions of nondeterministic finite automata for words of equal length

Davin Takahashi and Ethan Lamb

Ishigami and Tani studied VC-dimensions of finite automata. We show that their results apply to a new notion, lower VC-dimension, where all sets (instead of some set) of a given cardinality must be shattered. We also relate the VC-dimension to the Separating Words problem.

Savings from word powers in automatic complexity

Sun Young Kim and Clyde Felix

The automatic complexity of a word was introduced by Shallit and Wang in 2001 and studied further by Kjos-Hanssen since 2013. In this work we develop an implementation of a lower bound on the complexity involving occurrences of powers of words, such as the occurrence of “humu” twice in “humuhumunukunukuapua’a”.

tall-asl

Deontic Logic and proof assistants

Damir Dzhafarov, Stefan Kaufmann, Bjørn Kjos-Hanssen, Dave Ripley, et al., at the 2016 ASL Annual Meeting at UConn.

Slides

José Carmo and Andrew J.I. Jones have studied contrary-to-duties obligations in a series of papers.

They develop a logical framework for scenarios such as the following:

1. There ought to be no dog.
2. If there is a dog, there ought to be a fence.

One conjecture from Carmo and Jones 1997 was refuted in a rather technical way in my 1996 term paper at University of Oslo.
The conjecture stated that one could simply add the condition
$\DeclareMathOperator{\pii}{ob}$
$$
(Z \in \pii(X)) \land
(Y \subseteq X) \land
(Y \cap Z \ne \emptyset ) \rightarrow (Z \in \pii(Y )) \tag{5e}
$$
for the conditional obligation operator ob.
In a follow-up paper (2001) they argued that (5e) could be added by weakening some other conditions.
In a new paper in Studia Logica, and presented at the Association for Symbolic Logic Annual Meeting 2016 at UConn, I argue that (5d) and (5e) are in conflict with each other. The argument is a generalization and strengthening of the 1996 argument.

2018: Benzmüller et al. have implemented Carmo and Jones’ logic in the proof assistant Isabelle and Jake Fennick’s MA project is the implementation of my follow-up paper in Isabelle.

london1

Shift registers fool finite automata @ WoLLIC and in Discrete Mathematics

LFSRs (linear feedback shift registers) are popular pseudorandomness generators.
In a new project we show that they generate output (often called $m$-sequences) of maximal (nondeterministic path-based) automatic complexity. At this point we have an experimental result, one which would have probability $2^{-93}$ to occur “by chance”, as well as a theoretical but sub-optimal result.

Moreover, an $m$-sequence of length 31 provides an example of a word $x$ such that
$$
A^-(x)=A_N(x)+2
$$
where $A_N$ is nondeterministic path-based automatic complexity, and $A^-$ is non-total deterministic automatic complexity.
Such an example (where $A^-(x)-A_N(x)>1$) was not known before the consideration of LFSRs in this area. That consideration was an idea of Jason Castiglione.

The paper has been accepted at WoLLIC 2017 and in journal form for Discrete Mathematics (2018).

This project was presented at the poster session of the SIAM Conference on Discrete Mathematics 2016 in Atlanta, Georgia. The session was otherwise dominated by interesting work on RNA pseudoknots and chord diagrams (3 out of 6 posters) which in the case of the work of the Biocomplexity Institute researchers Ricky Chen and Thomas Li involves modeling with multiply context-free grammars.

WoLLIC 2017 slides

2326007202794064150-account_id=1

Superposition as memory @ UCNC17

Imagine a lock with two states, locked and unlocked, which may be manipulated using two operations, called 0 and 1. Moreover, the only way to (with certainty) unlock using four operations is to do them in the sequence 0011, i.e., $0^n1^n$ where $n=2$. In this scenario one might think that the lock needs to be in certain further states after each operation, so that there is some memory of what has been done so far. Here we show that this memory can be entirely encoded in superpositions of the two basic states locked and unlocked, where, as dictated by quantum mechanics, the operations are given by unitary matrices. Moreover, we show using the Jordan–Schur lemma that a similar lock is not possible for $n=60$.

Details in the paper: Superposition as memory: unlocking quantum automatic complexity which appeared in the Lecture Notes in Computer Science volume of the conference Unconventional Computation and Natural Computation (UCNC) 2017.

Slides

ASL Annual Meetings in North America

Midwest $n-2$ East $n-1$ West $n$ $n$
Western Illinois 2020
UIUC UConn Boise State 2017
UW Madison Waterloo, ON UC Boulder 2014
Notre Dame Washington, D.C.** UC Berkeley 2011
Montreál, QC U. Florida* UC Irvine* 2008
UIC Carnegie Mellon Stanford* 2005
UIUC U. Pennsylvania Las Vegas 2002

**invited plenary speaker
*special session speaker
attendee

group

Covering the computable sets

I participated in the workshop on Algorithmic Randomness in Singapore and the conference on Computability, Complexity and Randomness.

With host Frank Stephan and fellow participant Sebastiaan Terwijn we wrote a paper entitled Covering the recursive sets which appeared in Lecture Notes in Computer Science, Conference on Computability in Europe, 2015, and has now been published in Annals of Pure and Applied Logic.