Dr Pascal Bercher

Pascal Bercher
+61 (0)2 - 612 - 50 322



I am doing research in the fields of Hierarchical Task Network (HTN) Planning and Partial Order Causal Link (POCL) Planning. I'm interested in theoretical foundations (mostly complexity analyses), algorithms, and heuristics of/for those fields. For a more detailed description of my research interests see the respective tab or check out some of my papers.



PhD under my supervision

  • Scholarships/Funding: I have a fully funded scholarship available! Please apply!
  • Who can apply? Pretty much everyone, but I assume that you are are worth my time, so please don't let me down. Obviously, having attended courses like Artificial Intelligence (search, heuristics, planning etc.) would be invaluable, but also general computer science courses like Complexity Theory / Theory of Computation, or even Graph Theory could suffice. Just convince me that you have what it takes to be successful! I have high expectations from anybody I supervise, but in exchange I offer an for-me-unhealthy amount of supervision and guidance as payback. Also, my field is super-interesting, and there is a lot to explore, so take the opportunity!
  • How to apply? First of all, write your email with care, I do not want to see obvious mistakes and carelessness. Don't worry if you are not perfect in writing (or speaking) English, I do not care about this! But I care about the effort you put in. I will let you decide what to put into your application, but clearly I require a transcript and a few sentences about your background and why you would like to pursue a PhD under my supervision at ANU in the field of planning. I might then give you a very few papers to read so we can have an interview about it. Pass that and we see further.
  • Further information? Read the ANU PhD scholarship info page and some more information on ANU MPhil and PhD scholarships and applications.
  • PhD in planning at another University? If you are a great student, then of course I would love to supervise you! Sadly, there is always limited funding, so I cannot accept everybody. PhD positions in planning from everywhere around the world are regularly posted over the following two mailing lists, so you might consider subscribing them - only if your application with me is isn't successful! ;)
    • planning-list~AT~googlegroups.com. The is a general mailing list for planning.
    • icaps-conference~AT~googlegroups.com. This belongs to the ICAPS conference series, the premier conference on Automated Planning and Scheduling.

Before I joined ANU I was also involved in teaching at two other Universities: University of Freiburg, Germany (where I was still a student) and at Ulm University, Germany, where I did my PhD and (almost) two years of post-doc.


Lectures delivered


  • In S1 of 2021 (and following), I will be, together with Yoshihiro (Yoshi) Maruyama), the convenor of the lecture Logic (COMP2620/COMP6262/PHIL2080). I deliver the first half of the course, Yoshi the second.
  • In S2 of 2021, I held a guest lecture on AI in Games in Steve Blackburn's course Structured Programming (COMP1110). Slides. Video.
  • In S2 of 2021 I am the second examiner (the convenor is Hanna Kurniawati) of the lecture Algorithms (COMP3600/6466), where I teach weeks 6, 7, and 8 (25%).


  • In S1 of 2020, I held a guest lecture (2 hours, but stretched to 3 hours in the recordings to include more explanations) in the lecture Advanced Computing R&D Methods (COMP2550/4450/6445) by Jochen Renz. The lecture was on Theoretical Research Methods, with a focus on Heuristic Properties in Search and Classical Planning. Slides.
  • In S2 of 2020, I held a guest lecture on AI in Games in Steve Blackburn's course Structured Programming (COMP1110). Slides. Video.
  • In S2 of 2020, will give a guest lecture on Classical Planning in the Canberra Computer Science Enrichment course for high school students, organised by Josh Milthorpe. Slides. Hands-on material.

Lectures supported


  • 2021, S2 to 2022, S1: I am supervising one research project:
    • 24 pt Honours: On dead-end recognition in Sokoban and Planning (Co-supervisor, i.e. both are primary)
  • 2021, S2: I am supervising one research projects:
    • 12pt: -- kept secret until done -- (publication planned) (Primary supervisor)
  • 2021, S1 to S2: I am supervising one research project:
    • 24pt Honours: Integrating SAT Solvers into Heuristic Search (Secondary supervisor)
  • 2021, S1: I was or am supervising two research projects:
    • 12pt: Solving the Waiter's Tray Puzzle Using Classical and HTN Planning. (Co-supervisor, i.e. both are primary)
    • 6pt: On the Complexity of HTN Repair, Recognition, and Length-Bounded Plans (Sole supervisor)
  • 2020, S2: I supervised 4 research projects:
    • 6pt: Solving Minesweeper using Classical Planning with Global State constraints. (Secondary supervisor)
    • 6pt: Complexity Results for Fully Observable Non-Deterministic (FOND) HTN Planning. (Sole supervisor), published at ICAPS'21
    • 12pt: Solving the Waiter's Tray Puzzle Using Planning. (Co-supervisor, i.e. both are primary)
    • 12pt: Solving Puzzle Games Using Constraint Solvers. (Co-supervisor, i.e. both are primary)
  • 2020, S1 to S2: I supervised one 24 pt Honours research project:
    • 24pt Honours: On the Generation of User-Friendly Plan Linearizations. (Primary supervisor)


  • In S2 of 2021, I will serve as examiner of the following research projects:
    • 24 pt, in the context of heuristic planning for multiple objectives (started in S1)
    • 12 pt, in the context of planning and acting taking moral actions
  • In S2 of 2020, I served as examiner of two research projects
    • 12pt, in the context of SAT solving and protocol verification
    • 24pt Honours, in the context of planning under uncertainty

Ulm University

Lectures delivered:

  • In SS 2019 I delivered 5 lecture classes (25 % of the entire lecture) in the course Introduction to Computer Science.
  • In WS 2018/2019 I delivered a course on Hierarchical Planning that was conceptualised and delivered by myself.

Lectures supported

I was supporting my colleagues in several AI planning and foundational AI lectures. The lectures listed below are only those which I was responsible for (which includes creating the exercises and exams as well as being a lecturer of the respective exercise classes).

  • Intelligent Planning (SS 18)
  • Intelligent Planning (WS 17/18)
  • Intelligent Planning (SS 17)
  • Introduction to Artificial Intelligence (WS 17/18)
  • Introduction to Artificial Intelligence (WS 13/14)
  • Introduction to Artificial Intelligence (WS 12/13)
  • Introduction to Artificial Intelligence (SS 10)

Seminars organised and supported

I was a supervisor for one to three seminar participants in all of the following seminars:

Introductory Seminars:

  • Artificial Intelligence (SS 19) -- this seminar was organised by me
  • Artificial Intelligence (SS 18)
  • Artificial Intelligence (WS 17/18)
  • Artificial Intelligence (SS 17)
  • Artificial Intelligence (SS 16)
  • Artificial Intelligence (WS 15/16)
  • Artificial Intelligence (SS 15)
  • Artificial Intelligence (SS 13)
  • Artificial Intelligence (SS 12)


  • Advances in Artificial Intelligence (WS 17/18)
  • Advances in Artificial Intelligence (SS 17)
  • Artificial Companions (SS 16)
  • Advances in Artificial Intelligence (WS 13/14)
  • Advances in Artificial Intelligence (WS 12/13)
  • Advances in Artificial Intelligence (SS 12)

I did also do supervision

  • 3 Diploma or Master Theses (Diploma Theses do not exist anymore, they are essentially the same as Master Theses). Master Theses are essentially the same as 24 point Honours research projects at ANU.
  • 9 Bachelor Theses. A Bachelor theses can be regarded a bit more than a 12 point research project at ANU.
  • 5 Projects and Practicals. These can differ severely in their length and can be compared with either 12 or even 24 point research projects at ANU. The major differences are that they are focused on programming something, so there does not need to be any scientific research involved. Secondly, students are only required to write a "report" rather than a "thesis", which is not nearly as scientific and long as a thesis required to be.

University of Freiburg

While I was still a student of Computer Science at the University of Freiburg, I was a tutor for several lectures. There, being a tutor implied correcting exercises (and exams, but don't tell! :)) and being a lecturer of the respective practice groups. These are the respective lectures:

  • Formal Methods and Programming (WS 08/09, Lecture of Cognitive Science)
  • Foundations of Artificial Intelligence (SS 08)
  • Foundations of Artificial Intelligence (SS 07)
  • Computer Science I (WS 05/06)

As my doctoral thesis, my research interests span from theory to practice -- content-wise all is concerned with either Hierarchical Task Network (HTN) planning or Partial Order Causal Link (POCL) planning.

Hierarchical Task Network Planning

Short explanation of HTN planning: HTN planning is an approach to planning that's centered around problem decomposition. We are given an initial task network -- a partially ordered set of primitive or compound (or abstract) tasks. Primitive tasks are the actions known from classical planning, i.e. they specify preconditions and effects stating in which states they are applicable and how they chance a state if applied. Compound tasks are just abstracts of pre-defined task networks, so they are essentially just (parametrised) names like go(Canberra,Sydney). The planning model specifies rules how they can be achieved. These rules, called decomposition methods, are simply mappings to pre-defined task networks, which can in turn contain compound tasks. The goal is to refine the initial task network into a primitive one that is executable. HTN planning is more expressive than classical planning, where this mechanism of task decomposition does not exist. In its most general form (as just explained) it's undecidable.

My research interests in HTN planning are, roughly ordered by my interest:

  • Design of well-informed heuristics. (This is still a young field with only a limited number of heuristics available.)
  • Investigation of the computational complexity of various problems like the plan existence problem (how hard is it do decide whether there exists a solution?)
  • Essentially all questions that are related to incorporating human users into the loop. These comprise:
    • Plan abstraction and presentation (how can plans be presented on a more abstract level? can we stop planning on more abstract levels?)
    • Plan linearization and presentation (in which order should plan steps be presented to a human user so that the pan's execution order seems reasonable?)
    • Plan explanations (how to find reasonable explanations for plans and how they look like?)

Partial Order Causal Link (POCL) Planning

Short explanation of POCL planning: POCL planning is a technique for solving classical panning problems, where we would like to find a plan in order to achieve some (state-based) goals. In POCL planning, this is done in the space of partially ordered (also called non-linear) plans. Search is done in a regression-like fashion starting with the goals: select a condition not yet achieved (called "open") and select an appropriate action (i.e., with matching effect) from the plan or model and "document" that goal achievement by the insertion of a so-called causal link. Tis procedure is repeated until a goal plan has been found. Since search nodes are partially ordered plans (rather than states as in standard progression search), heuristic desingn is much more complicated.

Some more background of POCL planning: Since roughly 15 years this kind of problem solving is generally regarded outdated (some even say obsolete!) because state-based progression search is simply much more efficient nowadays. However, this argument is a purely empirical one. Moreover, there is a vast variety of well-informed heuristics in classical state-based planning, but almost none exist in POCL planning. Hence, it's interesting to imagine where POCL could be by now if we had as well-informed heuristics for that search as well. (Whether this can even be is another question, as some of my theoretical results indicate that heuristic design is computationally harder than in the progression setting.) Another important note to make is that POCL techniques are still used in hierarchical planning, as one of the few standard techniques for solving HTN problems relies on POCL planning techniques.

My research interests in POCL planning are, roughly ordered my interest:

  • Design of well-informed heuristics. (Again, almost no heuristics exist so far!)
  • Investigation of the computational complexity related to POCL plans (such as the plan existence or plan optimization.)

Practical application

Well, most that I am interested in is already covered above as part of HTN planning: When ever one integrates a human into the loop, several new questions arise that need to be addressed in a systematic way. For instance, once we have found a solution to a problem (i.e., a plan) that plan can be executed successfully as otherwise it wouldn't be a solution. However, for a human it might be a big difference in which order its actions are executed (by him or her) since there might be a switch of contexts that could be confusing or even annoying. Finding a reasonable (we called it "user-friendly") reordering is one such task that can be investigated on both a formal and an empirical level. Other related questions, as mentioned above, are the presentation of plans on higher levels of abstraction and the explanation of plans.

Another important aspect in the practical application of planning technology is the planning language's level of expressiveness. In order to solve real-world problems, we need to be able to express time (at the least!) or more generally functions. This will require new formalisms, reductions, and heuristics.

You can also find me on Google Scholar and in DBLP





Book chapters:



Conny Olz »

Best Paper Awards:

Best Reviewer Awards:

 To maintain anonymity, honours and awards for journals are listed at the end, in a meaningless order, without any year, probably severely outdated (also to maintain anonymity, like for journal reviewing).

  • AAAI 2021 Outstanding Program Committee Member
    13 out of 9493 program committee members (1.3 ‰) won this award.
  • AAAI 2019 Outstanding Program Committee Member
    6 out of 2201 program committee members (2.7 ‰) won this award.
  • Theoretical Computer Science Outstanding Reviewer Award (Elsevier journal)

Further honours and awards:

  • Cooperation Award: Science – Economy 2019
    The research project Do it yourself, but not alone: Companion-Technology for Home Improvement" that was coordinated by me for its entire runtime from 2016 to 2019 won Ulm University's "Cooperation Award: Science – Economy 2019" (German: Kooperationspreis: Wissenschaft – Wirtschaft 2019).
  • ICAPS 2019 Best Dissertation Award
    For my dissertation Hybrid Planning -- From Theory to Practice

    Award description from ICAPS website:
    The dissertation stands out by covering a lot of ground:
    1. It formalises and develops planning with hierarchical task networks (HTNs) toward a hybrid formalism that includes partial-order causal link planning;
    2. it presents complexity results for the resulting problem classes;
    3. it develops heuristics for hybrid planning;
    4. it describes the implementation of a hybrid planner and its integration into a companion device that assists in the set-up of a home theater system; and
    5. it performs a user study to evaluate the system. The dissertation also rekindled interest in HTN planning by putting it on firm formal ground and connecting it to recent developments in classical planning.
  • Nomination for the GI Best Dissertation Award 2017
    Ulm University nominated my dissertation for the GI Best Dissertation Award 2017, a national award (joint with the GI Germany, Switzerland, and Austria) for the best dissertation in the field of Computer Science. The GI (Gesellschaft für Informatik, eng: Society for Computer Science) encourages nominations that make progress in the field of Computer Science or related practical-oriented areas; they should further have some impact on the today's society. The final winners were announced here. My 10-page dissertation abstract (in German), as well as all other nominated dissertations, are published in the Proceedings "Ausgezeichnete Informatikdissertationen" (eng: Awarded Computer Science Dissertations).
  • Paper Presentation at Press Conference of AAAI 2015
    I was presenting my system demo paper "A Planning-based Assistance System for Setting Up a Home Theater" (AAAI 2015) at a press conference that was hold during the AAAI conference 2015. They selected five papers that are of interest to the public due to their relevance for today's society.



Reviewer for journals:
(Mostly severely outdated and years omitted -- both on purpose to maintain anonymity.)

  • Journal of Artificial Intelligence (JAIR)
    (at least 1 article)
  • Theoretical Computer Science
    (at least 1 article, awarded for outstanding reviewing)
  • IEEE Transactions on Systems, Man and Cybernetics: Systems
    (at least 1 article)
  • KI – Künstliche Intelligenz
    (at least 3 articles in a Special Issue on Companion Technologies for which I was a guest editor)

Reviewer for book chapters:

Senior Program Committee (SPC) member at conferences:

  • IJCAI: 2021
  • ICAPS: 2019, 2021-2022

Program Committee (PC) member at conferences:

  • IJCAI: 2013, 2019–2020*
    I've joined the IJCAI PC board for three years, 2021-2023
  • IJCAI-ECAI: 2018, 2022
  • ECAI: 2020
  • AAAI: 2015, 2017–2019*, 2021*
    (honored as outstanding PC member for AAAI 2019 and 2021)

Program Committee (PC) member at workshops:

  • HPLAN, i.e., Hierarchical Planning: 2018-2021 (I was also its chair)
  • WIPC, i.e., workshop of the IPC: 2021 (I was also an organiser)
  • XAIP, i.e., Explainable Planning: 2020

Reviewer for conferences (in addition to the PC/SPC memberships):

  • ICAPS: 2012, 2015–2018, 2020
  • ECAI: 2016
  • AAAI: 2012, 2014, 2020
  • KI: 2012–2013

Reviewer for workshops:

  • Computer Games Workshop: at IJCAI 2017

Reviewer for student conferences:


Invited talks:

Conference, workshop, and competition organisation, session chairing:

Further services to the AI community and the public:

  • Together with Daniel Höller, I gave the first Tutorial on HTN Planning at ICAPS 2018.
  • I was a guest editor for the journal "KI - Künstliche Intelligenz" for the Special Issue on Companion-Technologies, which appeared in February 2016.
  • I was in charge of creating a video that promotes a planning-based assistant for setting up a complex home theater. The video further explains the applied scientific technologies for a not necessarily scientific audience.

Services to the University

at the ANU:

  • In April 2021, I've joined the SOCO (School of Computing) PhD scholarship committee. (Not sure until when.) There are four rounds each year (two National, two International). Before joining the board as a regular/continuing member, I was a member of the RSCS (Research School of Computer Science) PhD scholarship committee for International Students (April round) in 2020.
  • In 2020, I volunteered to review at ANU Student Research Conference (SRC).

at Ulm University:

  • I was in the appointment committee for the new Assistance Professorship (German: Junior-Professor) in Explainable Artificial Intelligence at Ulm University, Germany in 2019.
  • From October 2016 to October 2019 I was the project coordinator for the technology transfer project Do it Yourself, but not alone: Companion-Technology for Home Improvement.

I use this page to make all downloads and links available that could be interesting and useful for some.

My Teaching 'Material'

Hierarchical Planning

  • Tutorial on HTN planning (from 2018) by me and my former colleague Daniel Höller
  • A video explaining how Hierarchical Planning can be applied to realise assistance support for complex reasoning tasks -- illustrated with a system that supports in the task of setting up a home theater. All deployed technologies (such as hierarchical planning) get explained tailored to a general non-scientific audience: Video

Classical Planning

  • Lecture slides introducing classical planning from scratch (from S1 2020), focusing on heuristic search, one 2-hour lecture: Slides
  • Lecture slides introducing classical planning from scratch (from S2 2020), focusing on modeling via PDDL, one 1.5-hour lecture with hands-on exercises: Slides. Hands-on material.

AI in Games

  • Since 2020 I give a guest lecture on AI in Games in Steve Blackburn's course Structured Programming (COMP1110).

    • S2 2021, one 1-hour lecure: Slides. The lecture was recorded, see below or on  YouTube

    • S2 2020, one 1-hour lecture: Slides. The lecture was recorded, see below or on YouTube

Theoretical Computer Science / Foundations of Computing

  • Lecture slides on Deterministic Finite State Automata (DFSAs; also called Deterministic Finite State Machines (DFSMs) and Deterministic Finite Automata (DFAs)), guest lecture held in early 2019, one 30-minute lecture: Slides

Various, mostly for students

  • Non-binding) marking guidelines for research project:
    • by John Slaney for 24pt. Honours projects [Links to be provided later]
    • by Zhenchang Xing for non-honours projects (any points) [Links to be provided later]
  • Material for students who are new to doing scientific research and scientific writing. Specifically: A presentation about how to search for scientific papers and another one about how to write a scientific work. An example seminar paper is given as well to provide an example on how to cite papers appropriately: download
  • My LaTeX files for slides using beamer: download
    Note that this design does formally not comply with the ANU style guides in the sense that it uses another corporate design (colors), but when you include the ANU graphics, the required "hard constraints" are fulfilled, so you should still be able to use it for ANU presentations (which I do, even for all my lectures).
  • Material to learn the basics of classical (non-hierarchical) planning. Read/work through in that order!
  • Material to learn the basics of hierarchical task network (HTN) planning. Read/work through in that order!
    • I assume that you are already familiar with classical planning. So follow the steps above first.
    • Then, I recommend to "start" with our IJCAI survey paper from 2019 on HTN planning, since it is written for non-experts, i.e., without much technical content. Disregard all contents about HGN or GTN planning, i.e., read until (uncluding) chapter 3.1.
    • After that, for more technical definitions, read the paper which introduced the simplistic HTN formalism, but only until section 2 (inclusive) to get the full technical definitions. If you know the basics of complexity theory, also read section 3.
    • By this point you should have understood the problem class of HTN planning, i.e., how is the problem defined, which includes which task networks are considered solutions and which are not. You should not be able to follow our tutorial on HTN planning, which explains all that in a bit more details (though only slides are available) and also explains some search algorithms for solving such problems.
    • You may now read unil (including) page 10 (Def. 4) of our JAIR 2020 article, after which you will understsand the standard (progression) algorithm for solving HTN problems.


Entertainment (not work-related!)

Although this is not a "private" webpage, I still decided to add some stuff that has pretty much nothing to do at all with work. Well, not directly, that is. It turns out that many computer scientists share a very similar humor. And here I share it with everybody! The second part is not on humar but education covering topics like medicine/biology (like vaccinations), physics/space travel/the universe, and even math.

Monty Python

Well, there are countless "Best of" lists you can easily Google for by yourself, so I don't see the point providing yet another list here. I just try to obtain a bit of "culture" by making aware of it! Simply it's so old already that current students stop even knowing it. So, I just give two of the most famous sketches (google for more!).

Fun fact: Did you know that the name of the programming language python is a tribute to Monty Python? There are further references, such as using "spam and eggs" in comments (etc.) instead of the typical "foo and bar". (see Wikipedia)


If you are a computer scientist (or a mathematician etc.), you very likely know these great comics, anyway! Still, here is a selection that's highly related to us (computer) scientists:

xkcd also features what if? (https://what-if.xkcd.com/) -- serious scientific answers to absurd hypothetical questions. (You might know this from the big bang theory... :))

PhD comics

Well, xkcd is (imho) worlds better, because it is really smart (and nerdy) humor. PhD comics are not "smart", but they tell the story of PhD students (or researchers, no much difference there, actually), so they are also great! Just for a different reason.

Education channels on YouTube

  • Kurzgesagt: An amazing YouTube channel covering all different kinds of scientific topics, most are related to physics and the Universe, but they cover many other topics like medicine as well. The name is German for "in a nutshell", but the content is English! (Though they've recently launched a German channel as well.)
  • VSauce: Another absolutely amazing YouTube channel! :) It covers so extremely many topics that it's hard to even describe it in the first place. They even cover technical topics like number theory, but also every-day topics like the placebo effect. What stands out is how entertaining it is despite explaining everything on a scientific level while still being easy to grasp.
  • Ted Talks: Some "private people" give an interesting talk about what they personally care about (in an interesting and entertaining way). Many are scientists or Professors, others are entrepreneurs. A very few people just seem to be self-promoters who like hearing them talk^^, bit the vast majority is actually quite amazing. Literally every topic is covered.
  • Last week Tonight: A comedy/entertainment show, but all the content covered is of an educational nature. Much of it is tailored to the USA, but many topics generalise. Although using
  • Adam ruins everything: Like Last week tonight, this is clearly entertainment and comedy, but again the content is educution. The show explains common myths, i.e., wrong every-day "knowledge". It also shows where certain traditions come from - most of the time "ruining" them. :)
  • There are some other "educating" channels that I like, though they are not that serious than the others, so I'm not mentioning them here publicly. :) You can ask me if interested!

Updated:  10 August 2021/Responsible Officer:  Head of School/Page Contact:  CECS Webmaster