Asta (Andreas) Halkjær From

I am a PhD student at DTU Compute since February 2020 working on Formally Correct Deduction Methods for Computational Logic, especially using the proof assistant Isabelle/HOL. My supervisor is Jørgen Villadsen and my co-supervisor is Nina Gierasimczuk.

I was a MSc student on the Honours Programme in Computer Science and Engineering at DTU from 2018 to 2020. My MSc thesis on Hybrid Logic was supervised by Jørgen Villadsen, Alexander Birch Jensen and Patrick Blackburn.

Presence elsewhere

GitHub

Twitter

Instagram

Goodreads

Articles

A Concise Sequent Calculus for Teaching First-Order Logic at Isabelle Workshop 2020
Asta Halkjær From, Jørgen Villadsen.

PDF
Formalizing a Seligman-Style Tableau System for Hybrid Logic (short paper)
Asta Halkjær From, Patrick Blackburn, Jørgen Villadsen.

To appear at IJCAR 2020.
Teaching a Formalized Logical Calculus in ThEdu'19 post-proceedings
Asta Halkjær From, Alexander Birch Jensen, Anders Schlichtkrull, Jørgen Villadsen.

DOI: 10.4204/EPTCS.313.5
Multi-Agent Programming Contest 2018 - The Jason-DTU Team
Jørgen Villadsen, Mads Okholm Bjørn, Andreas Halkjær From, Thomas Søren Henney, John Bruntse Larsen.

Lecture Notes in Computer Science, vol 11957, pp. 41-71. Springer.
Editors: Tobias Ahlbrecht, Jürgen Dix and Niklas Fiekas.

DOI: 10.1007/978-3-030-37959-9_3
A Verified Simple Prover for First-Order Logic at PAAR 2018
Jørgen Villadsen, Anders Schlichtkrull, Andreas Halkjær From.

PDF
Students' Proof Assistant (SPA) in ThEdu'18 post-proceedings
Anders Schlichtkrull, Jørgen Villadsen, Andreas Halkjær From.

DOI: 10.4204/EPTCS.290.1
Natural Deduction Assistant (NaDeA) in ThEdu'18 post-proceedings
Jørgen Villadsen, Andreas Halkjær From, Anders Schlichtkrull.

DOI: 10.4204/EPTCS.290.2
Substitutionless First-Order Logic: A Formal Soundness Proof at Isabelle Workshop 2018
Andreas Halkjær From, John Bruntse Larsen, Anders Schlichtkrull, Jørgen Villadsen.

PDF
Drawing Trees at Isabelle Workshop 2018
Andreas Halkjær From, Anders Schlichtkrull, Jørgen Villadsen.

PDF, Isabelle theory
Natural Deduction and the Isabelle Proof Assistant in ThEdu'17 post-proceedings
Jørgen Villadsen, Andreas Halkjær From, Anders Schlichtkrull.

Includes my work on translating online NaDeA proofs to the Isabelle encoding of the proof system.

DOI: 10.4204/EPTCS.267.9
Multi-Agent Programming Contest 2016 - The Python-DTU Team in IJAOSE 2018
Jørgen Villadsen, Andreas Halkjær From, Salvador Jacobi, Nikolaj Nøkkentved Larsen.

I did the initial work on the code used by the Python-DTU team for the Multi-Agent Programming Contest 2016.

DOI: 10.1504/IJAOSE.2018.10010604
Code Generation for a Simple First-Order Prover at Isabelle Workshop 2016
Jørgen Villadsen, Anders Schlichtkrull, Andreas Halkjær From.

PDF

Published formalizations

Epistemic Logic in Archive of Formal Proofs (October 2018)
Andreas Halkjær From

This work is a formalization of epistemic logic with countably many agents. It includes proofs of soundness and completeness for the axiom system K. The completeness proof is based on the textbook "Reasoning About Knowledge" by Fagin, Halpern, Moses and Vardi (MIT Press 1995).

Website Outline (PDF) Theory
A Sequent Calculus for First-Order Logic in Archive of Formal Proofs (July 2019)
Andreas Halkjær From

This work formalizes soundness and completeness of a one-sided sequent calculus for first-order logic. The completeness is shown via a translation from a complete semantic tableau calculus, the proof of which is based on the First-Order Logic According to Fitting theory. The calculi and proof techniques are taken from Ben-Ari's Mathematical Logic for Computer Science.

Website Outline (PDF) Main theory
Hybrid Logic in Archive of Formal Proofs (December 2019)
Asta Halkjær From

The formalization accompanying my MSc thesis.
The development version contains the latest results.

Website Outline (PDF) Main theory
IsaFoL: Isabelle Formalization of Logic
I have contributed to a number of formalizations in the IsaFoL project:

Abstracts

Formalized soundness and completeness of natural deduction for first-order logic at SLS 2018
Andreas Halkjær From.

Abstract, Slides
Teaching first-order logic with the natural deduction assistant (NaDeA) at SLS 2018
Andreas Halkjær From, Helge Hatteland, Jørgen Villadsen.

Theses

BSc: Formalized First-Order Logic (July 2017)
My BSc thesis on formalizing the soundness and completeness of NaDeA in Isabelle/HOL.

Report, Slides (Danish)
MSc: Hybrid Logic (January 2020)
My MSc thesis on formalizing the soundness and completeness of a Seligman-style tableau system for hybrid logic in Isabelle/HOL.

Thesis, Slides

Talks

FIT – From's Isabelle Tutorial – Verification of Quicksort (October 2017)
A fast-paced, hands-on introduction to Isabelle/HOL I gave at PART DTU.
Magnolia – Implementing System F with Anonymous Sums and Products (March 2018)
Overview of the Complete and Easy Bidirectional Type Checking for Higher-Rank Polymorphism paper as well as my own additions. Also briefly describes Abstract Binding Trees. Given at DTU.
Using the Isabelle Proof Assistant: Seligman-Style Tableau for Hybrid Logic (September 2019)
The Isabelle proof assistant can be used to mechanically develop and check results in logic, mathematics, computer science etc. In this talk I motivate this process and explain how it looks in practice for a basic hybrid logic. The running example will be preliminary work on the completeness and termination for a Seligman-style tableau system by Blackburn, Bolander, Braüner and Jørgensen.
Given at The LogicS of Prior Past, Present, and Future at Roskilde University.
The Isabelle Proof Assistant and Hybrid Logic: Formalizing Seligman-Style Tableaux
Update on my MSc thesis work. Given at an AlgoLoG seminar at DTU.

Software

A Pretty but not Greedy Printer (January 2018)
My implementation of Jean-Philippe Bernardy's A Pretty But Not Greedy Printer (Functional Pearl). PACMPL 1(ICFP): 6:1-6:21 (2017) in OCaml. The author of the paper has a version in Haskell.

GitHub, OPAM
Sudoku Solver (June 2016)
A solver for large Sudoku puzzles which we wrote as a fourth-semester final project. Solving is done either using our own backtracking tactic solver or with an external SAT solver by compiling the problem into the CNF-format DIMACS. The GitHub page includes an abstract in English.

GitHub, PDF (Danish)
The Playground (December 2015)
My solution to an internal programming competition in the Algorithms and Data Structures 2 course at DTU. The readme includes a description of the problem and my algorithm as well as fully annotated version of the C code.
GitHub

Experience

Teaching Assistant

I am or have been a TA in the following courses:

02101 Introductory Programming, fall 2015
02105 Algorithms and Data Structures 1, spring 2016
02101 Introductory Programming, fall 2016
02110 Algorithms and Data Structures 2, fall 2016
02105 Algorithms and Data Structures 1, spring 2017
02180 Introduction to Artificial Intelligence, spring 2018
02156 Logical Systems and Logic Programming, fall 2018
02156 Logical Systems and Logic Programming, fall 2019
02102 Introductory Programming, spring 2020
02256 Automated Reasoning, spring 2020

I have also helped teach kids aged 9-12 years old game programming in MIT Scratch at Hello World.

Research Assistant

I worked as a research assistant at DTU Compute from August 2017 to December 2017, working with Isabelle and NaDeA, especially translating students' proofs in NaDeA to their encodings in Isabelle.