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Name Arrival Schiphol Dinner on Sunday Shares with Remarks Leave Taxi
RolandBackhouse Sunday, arrived          
Patrick Bahr Sunday, ???? - Yes     Friday, Assen, 14:00 13:00
Richard Bird Sunday, Assen 18:27 - Yes     Saturday, Assen, 12:30 12:00 (s)
JeremyGibbons Sunday, Assen 18:27 - Yes     Saturday, Assen, 12:30 12:00 (s)
Walter Guttman Sunday, arrived - Yes     Friday, Assen, 12:00 11:00
FritzHenglein Sunday, Assen 21:27 ?? 18.50 Yes     Friday, Assen, 14:00 13:00
Ralf Hinze Sunday, arrived - Yes     Friday -
Peter Hoefner Sunday, arrived - Yes     Friday 13:00
Zhenjiang Hu Sunday, Assen 18:35 from Frankfurt No   Leaves Wednesday Wednesday -
Cezar Ionescu Sunday, Assen, 18:02 - Yes     Friday, Assen 13:00 11:00
JohanJeuring Sunday, arrived - Yes     Friday -
PatrikJansson Sunday, arrived - Yes     Friday, Assen, 12:00 11:00
Andres L\xF6h Saturday, arrived - Yes Clara and Aura   Saturday, Assen, 14:00 13:00
Jos\xE9 Pedro Magalh\xE3es Sunday, Assen ???? - No     Friday, Assen -
Lambert Meertens Sunday, arrived - Yes     Assen, 14:00 13:00
Bernhard Moeller Sunday, arrived - Yes     Friday, Assen 13:00 13:00
Conor McBride Sunday, arrived - Yes     Friday  
Conor McBride Sunday, arrived - Yes     Friday 13:00
Tom Schrijvers Sunday, arrived - Yes     Friday -
Wouter Swierstra Monday, Assen, 13:00 - No Friday, Assen, 14:00 13:00
Janis Voigtlaender Sunday, arrived - Yes     Friday -


Meng Wang

Organizational and administrative matters

Friday morning, March 28, 2014.

These private matters are not recorded in the public version of the minutes.

Formal resolution
The members of WG2.1 and the observers present at the 71st meeting, in Zeegse, The Netherlands, wish to thank Doaitse Swierstra of Utrecht University for looking after us with such consideration and hospitality. We were well cared for, and very well fed. Beverages, on the other hand, might have been a cause for concern\x85 Groningen has closed every last one of its 70 breweries; its Prinsenhof Hospital deliberately increased the height of its \x93gin wall\x94, to control drinking; and the Martini Kerk is disappointingly devoid of aperitifs. But any concerns we might have had were non-well-founded: the hotel went out of its way to encourage us not to drink the water, despite being situated right beside the River Water itself. Defensive measures notwithstanding, the city apparently still has need of a Drunkard\x92s Tower; and we were glad to hear that the Swierstra family is planning to re-establish the brewing tradition.

Next meetings
The 72nd meeting will probably be held in Vermont around December 8 - 12, 2014 at Robert Dewars house. August 24 - 28, 2015 Patrik suggests to visit G\xF6teborg, and May 16 - 20, 2016 Conor offers to organize a meeting in Scotland. After this 74th meeting we might go to Uruguay, Australia, or China.

Technical presentations in scheduled order

$ Conor McBride, Syntaxes not datatypes ( before, after) (Monday, March 24, 2014, 10:42): Inductive datatypes are just the closed terms of syntaxes which happen to involve no variable binding. Far too much effort is spent rediscovering the syntactic structure of datatypes which happen to represent terms. In this talk, I show how to define a universe of datatypes which represent syntaxes with variable binding and develop their substitution structure once for all. The well typed terms of the simply typed lambda calculus are directly and precisely encodable in this universe.

$ Cezar Ionescu, Calculating scientific programs? (Monday, March 24, 2014, 11:52): I discuss specifications for scientific programs and problems which arise in the attempt to calculate implementations from these specifications.

$ Richard Bird, An exercise found in a book on Algorithmics (Monday, March 24, 2014, 14:32): No abstract provided

$ Fritz Henglein, From querying to linear algebra and back (Monday, March 24, 2014, 15:19): No abstract provided

$ Patrick Bahr, Calculating correct compilers (Monday, March 24, 2014, 16:52): We present a new approach to the problem of calculating compilers. In particular, we develop a simple but general recipe that allows us to derive correct compilers from high-level semantics by systematic calculation, with all the required compilation machinery falling naturally out of the calculation process. Our approach is based upon a new application of well-known transformation techniques, and has been applied to calculate compilers for a wide range of language features and their combination, including arithmetic, exceptions, local and global state, various forms of lambda calculi, bounded and unbounded loops, non-determinism, and interrupts.

$ Bernhard M\xF6ller, GISCal - functional and relational models of some GIS aspects (Tuesday, March 25, 2014, 9:02): Geographic Information Systems (GIS) form a main focus of interest at the Augsburg Geography Institute. The authors have offered a joint course on functional modeling of GIS based on Haskell. In the coming summer semester its third issue is due. As the topic to model we have foused on Tomlin's Map Algebra and a generalistaion developed by the group of Camara. However, this model is too rigid in several aspects and also hard to follow by the students, the course is intended to be manageably by students who have no programming experience at all. The first part of the talk presents that model and dicusses possible varitions or revisions to make the topic more accessible.

During the internal discussions at Augsburg it turned out that a second topic of interest might be an approach to the modeling of spatio-temporal movement by Hendricks et al. This involve modalities such as "may" and "must" when describing movement in a geographic space. While the treatment in the original paper is only semi-formal, in the second part of the talk we show how to model these notions in relational algebra with box and diamond operators. They allow then expressing compulsions such as "we must reach the airport before the plane leaves" and avoidance of boundaries such as "we must not pass through road X because of construction work".

Since the abstract algebraic versions of box and diampnd can be used to give general semantics for CTL/CTL* and LTL, the approach should allow developing general spatio-temporal logics for GIS.


G. Camara, D. Palomo, R. Souza, O. Oliveira. Towards a generalized map algebra - principles and data types. In Workshop Brasileiro de Geoinform\xE1tica, 7, 2005, Campos do Jordao, Nov. 2005.

M. Hendricks, M. Egenhofer, K. Hornsby. Structuring a wayfinder's dynamic space-time environment. In W. Kuhn, M. Worboys, S. Timpf (eds.), Conference on Spatial Information Theory (COSIT '03), Kartause Ittingen, Switzerland. LNCS 2825. Springer 2003, 75-92

$ Tom Schrijvers, Effects and effect handlers (Tuesday, March 25, 2014, 10:54): No abstract provided

$ Peter H\xF6fner, Algebras for (automatic) verification of graph algorithms (Tuesday, March 25, 2014, 13:49): No abstract provided

$ Jos\xE9 Pedro Magalh\xE3es, Generic generation of constrained random data (Tuesday, March 25, 2014, 15:20): Generating data is useful, not only for testing purposes, but also for creating example data, for instance. Generic data generation gives us the usual advantages of generic programming; we have to write less code, and our generator is robust to changes in the datatype. But generic programs typically depend only on the structure of the type, and are agnostic to any semantics of the underlying data. However, when generating data, we often want to impose restrictions that are more semantic than structural; sorted lists, balanced trees, or valid ASTs, for example. In this talk I look at how to combine a generic data generator with user supplied constraints.

$ Walter Guttmann, Unifying approximation (Tuesday, March 25, 2014, 16:47): In this talk we look at various models of sequential computations. They differ in how precise they are and in the kinds of executions they can represent. Nevertheless they support the same program constructs, which satisfy many laws that we capture using algebras. We look at examples of algebras for iteration and for the states from which a computation has an infinite execution, based on which we define an approximation order. The various computation models are instances of the algebras. Program transformations, refinements and other theorems derived from the axioms hold in all these models. The algebras have also helped to establish an approximation order for a model for which they were not originally designed. The theories are implemented in Isabelle/HOL using its integrated automated theorem provers.

$ Patrik Jansson, An algebra for parallel parsing (Wednesday, March 26, 2014, 9:02): ( File1, File2)

$ Janis Voigtl\xE4nder, Embarrassingly simple generation of free theorems (Wednesday, March 26, 2014, 11:00): Presenting a simple generation scheme for free theorems (statements derived from polymorphic function types), which avoids unfolding of relational expressions and subsequent simplifications. During the talk, it turned out that the scheme is closely related to what dinaturality gives.

$ Jeremy Gibbons, Entangled state monads (Wednesday, March 26, 2014, 11:36): We present a monadic treatment of symmetric state-based bidirectional transformations, and show how it arises naturally from the well-known asymmetric lens-based account. As a step towards a unifying account of bidirectionality in general, we exhibit existing classes of state-based approaches from the literature as instances of our new constructions, investigate composition of entangled state monads, and sketch out notions of equivalence and the combination of bidirectionality with other computational effects. (joint work with Faris Abou-Saleh, James Cheney, James McKinna, Perdita Stevens)

$ Roland Backhouse, Overcoming non-distributivity (Thursday, March 27, 2014, 9:56): No abstract provided

$ Wouter Swierstra, Auto in Agda - Programming proof search (Thursday, March 27, 2014, 11:29): No abstract provided

$ Ralf Hinze, Mamamorphisms (Thursday, March 27, 2014, 14:00): The past decades have witnessed an extensive study of structured recursion schemes. A general scheme is the hylomorphism, which captures the essence of divide-and-conquer - a problem is broken into sub-problems by a coalgebra; sub-problems are solved recursively; the sub-solutions are combined by an algebra to form a solution. In this talk we introduce a simple toolbox for assembling recursive coalgebras, which by definition ensure that their hylo equations have unique solutions, whatever the algebra. Our main tool is the conjugate rule, a generic rule parametrized by an adjunction and a conjugate pair of natural transformations. Each seminal adjunction induces a useful recursion scheme. In fact, almost every structured recursion scheme seems to arise as an instance of the conjugate rule.

$ Johan Jeuring, Type-Changing Rewriting and Semantics-Preserving Transformation (Friday, March 28, 2014, 10:30): We present an approach to automatic program transformation that enables type-changing rewriting in a way that is type-safe and semantics-preserving. Simple rewrite rules, as inputs to the system, can change the types of terms and their free variables. A program transformation, derived from the language's type system, applies the rewrite rules and ensures that the source program and the rewritten target are always related. That relation enables the proof that the source and target of a complete transformation are equivalent.

In this talk, we describe the type-and-transform system for the lambda calculus with let-polymorphism and general recursion. We provide motivation and context with several relevant examples from the literature, and we establish and prove typing and semantic correctness properties of the system.

Meeting information

The meeting will be held in Zeegse near Assen/Groningen, the Netherlands, March 24- 28, 2014.


The exact location of the meeting is De Zeegser Duinen

Telephone: +31 (0)347 - 750 466

How to get there

Zeegse by Plane

You are most likely to fly to Schiphol, from where you can taken a train to Assen (either direct, or with one change). Trains run twice an hour, until very late at night. You can find the schedule here; select Schiphol as your starting point and Assen as your final destination.

The nearest airport is Eelde/Groningen, which is served by Transavia and Ryan Air. If you happen to be located near Milan this might be an option.

Assen by Train

At the airport train tickets can be bought from the machine in e.g. the bagage claim area with a lower chance to be pickpocketed than in the large central hall above the train station.

The Dutch railways have a special deal: a so-called "group ticket", which makes travelling quite cheap. I bought a 10 person group ticket for 65 euro's, which make it possible to travel from ANY PLACE in the Netherlands to Assen (and back on the same day, but you do not want that!). The instructions are in Dutch, so I think the easiest thing to do, is that you email me your:

Full name and date of birth

if you are interested in one of these tickets (at 6.50 each, instead of approx 25 euro's for a second class ticket). I will then try to get the ticket out of the system and in your email. You print it yourself, and you do not have to buy a ticket at the station. In case more than 10 people need a ticket I can order more on Friday evening, but they will probably a bit more expensive (but always less than 12 euro) since I do not expect that 20 people will need one. SO IF YOU ARE INTERESTED let me know as soon as possible. If things work out as expected we can do the same for the way back.

UPDATE: All the people who have expressed interest in such a ticket should have receivdd their. The first batch of 10 is sold out.

Internet in the train

All Dutch intercities provide free internet on the train. You select the tmobile network, which will take you to a page where you find the train schedule, and a tick box asking you to accept their conditions. Once you click the connect button you will be able to browse and send and receive mail. You can also go to the page: to find out whther you may have to switch trains anywhere (in about 50% of the cases).

You may try to reach me using Skype. My user name is doaitse.

Assen/Zeegse by taxi

Since there is no public transport in Zeegse the area is served by the so-called Regiotaxi from Assen, which costs 6.1 euro, and an extra adiscount of 50% for every next passenge. The ride takes approximately 20 minutes. YOU HAVE TO PAY THE DRIVER IN CASH. If you get money at the airport Schiphol it is probably best to go to a blue shop called AH to go, of which there are two in tha arrival hall, buy a coffee for 1.5 euro using the 50 euro note you are probably carrying, and make sure that your change is such that you can pay the taxi driver.

OUTDATED: The rules are simple. You have to call them one hour before your train arrives in Assen at 0031 (0) 592373111, or you press the Regiotaxi button at the taxi-stand at the front of the station (picture to be provided). They will pick you up within 15 minutes.

NEW TAXI INFORMATION: You have to call the taxi from Assen to the hotel in Zeegse at least one hour in advance. The tomobile connection in the train (see above) will tell you what time you will be in Assen. The new number you have to call is +31 900 400 2000. It appears that the municipality has decided to remove the push button at the station in preparation for a new system; since there is no agreement yet about what this new system will be they have not installed a new button. I deeply apologize for this. Given the fact that the phone call you will have to make is probably more expensive than the taxi ride I have came up with the following two solutions:
  • you send me a text message at +31 6 46136929, with your name(s) and arrival time, and I will make the reservation for you
  • you send me an email with your arrival time and I will make the reservation The taxi may pick up other persons too.

If you get out of the station at the main entrance (you went down the stairs and came up again on the west side of the station) you will first see some commercial taxi's. Do not take these. They will cost you quite a bit more. Move north, until you find the pole where the button has been removed from. The old picture in google maps looks like this. The name of the taxi service has changed to Regiotaxi. I will try to make a new picture today.

For the way back we have to make a schedule since they may have to employ some mini buses to get you all back to the station.

Zeegse by Car

Take the A28 to Assen, continue to Groningen and get off at the exit Vries/Tynaarlo/Zuidlaren and continue to Zuidlaren. Directly after crossing the railroad Assen-Groningen turn right towards Zeegse. After one kilometer follow the signs to the left.

Zeegse Tourist Information

Zeegse is located in the middle of the national park De Drentse Aa, and is a great place to start your walks or bicycle tours. The hotel has a small swimming pool and rents out bicycles. Cycling to either Groningen or Assen will be about 15 kilometres.

Registration and accommodation

Please fill in the Registration Form and mail it to me mentioning "reservation Zeegse" in the subject. I will confirm your message, add you the list of participants and forward it to the hotel. We have blocked 30 hotel rooms until January 13.

The conference fee includes a 7 euro insurance which covers calamities in case the meeting has to be cancelled or you have a personal issue (according to the standard Dutch hotel agreement) which prevents you from attending after you have booked.


Accommodation and drinks outside the meeting (i.e. during lunch or dinner as well as in the evenings) are to be paid directly to the hotel (on the day of departure). The hotel accepts cash (Euros, of course), Visa-Card, Mastercard (no American Express!), and ATM Card (bank card).


The hotel provides free internet access. You are encouraged to bring your laptop. Note that there is a no-computers rule (which includes tablets and smartphones!) during talks.


On Wednesday afternoon we will make a trip to the city of Groningen, have a boat tour there and visit the museum (Dutch participants who have Museum jaarkaart might want to take that with them). Approximate costs: 35 euro

Dinner on Thursday

On Thursday evening I am "inviting" you to my home (about a 30 minutes walk from the hotel) for drinks and dinner. The meal will be prepared by two (semi)professional cooks. The cost is 30 euro p.p. I will provide sufficient wine etc. I can arrange for a taxi/bus. Please let me know whether you want to walk or be transported or if you will not attend the dinner.

Latest information

  • In case of emergency on the day of arrival, here are a few telephone numbers where you may try to get help (The numbers are for use within the Netherlands, from outside the Netherlands you first have to dial the country code 0031 and skip the leading 0):
  • Hotel Zeegser Duinen: 0347 - 750 466
  • Regio Taxi in Assen: 0592373111
  • Doaitse Swierstra: (home)0592853221, (mobile) + 31 6 4613 6929:

  • In case you do not take dinner on Sunday, please indicate so on the form; you will not have to pay for it.

Meeting programme

Schedule (subject to change)

We will start at 9:00 on Monday and finish at noon on Friday. Please arrange to be there for the full meeting.

Monday, Tuesday, and Thursday, the schedule is as follows:

  • session - 9:00 to 10:30
  • coffee break - 10:30 to 11:00
  • session - 11:00 to 12:30
  • lunch - 12:30 to 14:00
  • session - 14:00 to 15:30
  • coffee break at 15:30 to 16:00
  • session - 16:00 to 18:00
  • dinner - 19:00 to ...


Groningen. ( Five members on a terrace.)


Will be announced.


I will have to make some further plans for the formal dinner and the excursion. These costs are not included yet; between 50-100 euro, and to be paid to me.

-- JeremyGibbons - 18 Oct 2013
Topic attachments
I Attachment Action Size Date Who Comment
GISWG21.pdfpdf GISWG21.pdf manage 485 K 27 Mar 2014 - 08:17 JohanJeuring  
backhouse-zeegse.pdfpdf backhouse-zeegse.pdf manage 1 MB 27 Mar 2014 - 10:27 JohanJeuring  
bird-zeegse.pdfpdf bird-zeegse.pdf manage 422 K 27 Mar 2014 - 11:22 JohanJeuring  
conor_after.pdfpdf conor_after.pdf manage 144 K 27 Mar 2014 - 08:08 JohanJeuring  
conor_before.pdfpdf conor_before.pdf manage 137 K 27 Mar 2014 - 08:09 JohanJeuring  
gibbons-zeegse.pdfpdf gibbons-zeegse.pdf manage 105 K 28 Mar 2014 - 16:56 JohanJeuring  
groningen-walk.jpgjpg groningen-walk.jpg manage 150 K 31 Mar 2014 - 11:09 JohanJeuring  
guttmann-zeegse.pdfpdf guttmann-zeegse.pdf manage 236 K 28 Mar 2014 - 10:54 JohanJeuring  
henglein-zeegse.pdfpdf henglein-zeegse.pdf manage 382 K 28 Mar 2014 - 17:07 JohanJeuring  
hinze-zeegse.pdfpdf hinze-zeegse.pdf manage 93 K 27 Mar 2014 - 15:06 JohanJeuring  
hoefner-zeegse.pdfpdf hoefner-zeegse.pdf manage 3 MB 27 Mar 2014 - 11:19 JohanJeuring  
ifip71_janis.pdfpdf ifip71_janis.pdf manage 204 K 27 Mar 2014 - 07:57 JohanJeuring  
ionescu-zeegse.pdfpdf ionescu-zeegse.pdf manage 355 K 27 Mar 2014 - 11:14 JohanJeuring  
jeuring-zeegse.pdfpdf jeuring-zeegse.pdf manage 303 K 31 Mar 2014 - 13:17 JohanJeuring  
schrijvers-zeegse.pdfpdf schrijvers-zeegse.pdf manage 2 MB 27 Mar 2014 - 13:37 JohanJeuring  
wswierstra-zeegse.pdfpdf wswierstra-zeegse.pdf manage 106 K 28 Mar 2014 - 16:59 JohanJeuring  
Topic revision: r70 - 17 Jul 2014, JohanJeuring
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