Dutch / Nederlands
Site map

I write, therefore I am

With this variation on a famous statement by the philosopher Descartes, I would like to express that the act of writing about what happens in my life is important to me.

Thursday, February 14, 2019

Exact Cover to SAT

Thinking about the Octopluszle and the lack of succes of making any progress, I decided to see if converting the problem into a Boolean satisfiability problem would be an option, knowing that there is a lot of research going on SAT solvers. I came across Solving Exact Cover via SAT, which happens to be from the same person who tried to solve the Octopuszle with an Exact Cover solver almost a year before. We could conclude from this, that he did not make much progress and that the Octopuszle is indeed a very hard puzzle.

Wednesday, February 13, 2019


Last Monday, I came across the China Labyrinth and the Octopuszle. Yesterday, I wrote a program to generate an Exact Cover for this problem and last night I ran my Exact Cover solver on it, but it did not find any solutions. Today, I discovered that others tried it before and did find solutions using a Python 3 Exact Cover solver. This was also refered to in a Hacker News thread about Organicity in abstract strategy games. Anneke Treep discussed it in the March and July 1990 issues of Cubism For Fun newsletter.

Saturday, February 10, 2019


I have installed Unbutu on johan. I installed it on the disconnected hard-drive that I put in place as an anti-virus back-up. It appeared that this drive was also seen as the first drive. So, now johan is a dual-bootable PC. I noticed that Firefox does not run very smooth under Unbutu and that it having similar problems with playing videos, like it has under Windows XP. I would think that it is related to my graphics card not being fully supported anymore.

Friday, February 8, 2019

Memoral service Martin Medema

Yesterday, I got news that Martin Medema died during the night of Monday to Tuesday and that there would be a short memoral service this morning. I doubted a long time whether I should go, because it was on Friday, June 12, 2009 that I met him for the last time. I met him shortly after I arrived at the University of Twente, usually at (board) game club Fanaat. I am happy that I did go. I discovered that until recently (when he became ill), he was a frequent guest at Fanaat. Almost half of the attendees where current members of Fanaat, students of the University. But there were also some people from the early eighties, some of which had not seen Martin for much longer than me. Arjan and Erik, as long time members of Fanaat, also attended. (The only person, I had expected to see, did not come.) Someone from the eighties had brought a seven hexes segment and placed it on the coffin with six wooden round stones of different colour on top of it. These are used in the game Atlantis. After the nephew of Martin said some words, several other people said some words, often telling how Martin had taught them important lessons in life, about trusting and living an alternative, nomadic life-style.

Thursday, February 7, 2019


This evening, I went to see the exhibition I owned a tree by Linda Vilka at the Tankstation in Enschede. Later, I also went to Concordia and saw the exhibition Inktspot of a hunderd political cartoons from Dutch newspapers. I also played a little with some musical art works that are part of the exhibition Ik zie ik zie wat jij niet hoort (I see what you do not hear), which is geared towards children.

Wednesday, February 6, 2019

Steered by technology

This evening, I went to Tetem art space to listen to the talk Gestuurd door techniek: Meegaan of weerstand bieden? (Steered by technology: Go with it or resist it?) by Peter-Paul Verbeek. The talk started a little late. (I wrote the following during the talk. It is my intepretation of what the speaker said.) Yesterday there was a news item about parents tracking children (through their mobile phones). It turned out that actually quite a number of parents are doing this. Parents think that it is go to use this technology. Another example is how people are always on their smartphone. There were also technology designed to steer us, such as speed cameras. There are also people against them and even destroy them. But these people do not realize that the roads are also designed in such a way that they control our behaviour. Why we do not design cars such that they cannot drive too fast. Probably, many people would be against this, because they would feel that it limits their autonomy. Speed bumps are also designed to change our behaviour: to make us brake our speed. Nowadays, we have the problem with fake news. Social media have started to control our thoughts. The first industrial revolution was the first large scale experiment with technology. Marx realized how this was tied in with capitalism. The movie Modern Times wanted to show that technology is steering people: how people become slaves of the machines. Currently, we are said to be in the fourth industrial revolution. Now there are also people who are against it. What is a stake now? We would like to split the world into subjects and objects. But maybe it is not possible to make such a clear a cut. Probably, they are always intertwinned. We create technology, but technology also change us. Technologies are often used for moralisation. Hans Achterhuis came with the proposal to moralisation of machines. People critized him about this. But that this week, there was a very big traffic accident on the high way due to heavy fog. The book Nudge by Richard H. Thaler and Cass R. Sunstein. 80% of the choices we make are habits. Maybe only 10% of our choices are conscious choices. There are very subtile ways to influence the behaviour of people. Persuasive Technology by B.J. Fogg. To use technology to persuate you in a certain direction. About autonomy. Technology is so much a part of our life, that we cannot escape it. Think, for example, think about the birth controll pill. It has had such an influence on our ethics. Kant said that the three big questions are: What can I know? What should I do? And what can I hope for? Technology has given us some answers on these questions. Steven Dorrestijn said that technologies work in four areas: Before the eye (persuasion, suggestion), to the hand (coercion, mediated gestures), behind the back (trends, user configuration), and above the head (utopian technology, dystopian technology). There are two axes about influence: from hidden to apparent and from weak to strong. Resulting in four quadrants: Coercive, persuasive, seduction, and decisive. The last is maybe the most scarry. Design mediations. You have a social goal: you want to have some desired behaviour. From this you have to design technology that encourage this behaviour. Design for environmental behaviour. Some one form Taiwan made him realize how much we here in the West are attached to our autonomy, even if it is clear that in the future it will destroy our world and make autonomoy completely irrelevant.

After the talk, I made some mention of the book On Photography by Susan Sontag to the speaker. Afterwards, I found it a pitty that the speaker did not address the possible impact of AI on our lives in the coming twenty years.

Björn Zielman

I went to the opening of the exhibition of Björn Zielman at B93. His exhibition also contained paintings by his mother Lammie and sculptures by his aunt Nancy. I also met with two of the members of Heliophile. One of them, under the artist name AcheFace, gave a performance on a modular synthesizer. I also met some other people and talked with them. I stayed for about an hour.


Tuesday, February 5, 2019


Today is the first day of the year of the pig according to the Chinese calendar. The spring festival has begun.

Hexagon numbers

This morning, I wondered what are all the areas that you can create with a (possibly irregular) convex hexagon on a triangular grid. The smallest such a haxagon consists of six triangles. By extending one side with four triangles, you get an irregular convex hexagon of ten triangles. It seems that there are some considerable gabs. I wrote a small program to find all sizes below a hunderd, and it found that the following sizes (larger than six) are not possible: 7, 8, 9, 11, 12, 15, 17, 20, 21, 23, 29, 36, 39, 41, 44, and 84. I was surprised about the lonely 84 and wondered whether there might be another much higher lonely number. Also wondered whether it would be possible to proof that above a certain number, all numbers occur as the size of such a hexagon. This evening, I realized that it is probably easy to proof this. A triangle grid is equivalent with a square gird with one diagonal added. Then every hexagon fits in a rectangle where two opposite corners have a triangle removed. The number of triangles in the rectangle is twice the height times the width. The size of the triangles that are removed is equal the square of the size (along the side of the rectangle). Because there are two corners, the combination of values that can be substracted increases with a power of two by the smallest height or width. Thirtheen is the first number, where there all the combinations is sufficient. Or in other words, for each number from 336 and above, there is a rectangle of height thirteen and a width equal or larger than thirteen with some corners removed with the required number of triangles. I wrote a program to verify this.

Monday, February 4, 2019

The Red Line

This evening, I saw the exhibition The Red Line at the Vrijhof building of the University of Twente. This exhibition shows pictures taken by the members of Amateur Photographers Association Drienerlo Foton around the theme of a red robe, which occurs in almost all pictures, and in the exhibition connects the pictures.

Sunday, February 3, 2019


Saturday, February 2, 2019

Exhibitions and books

This afternoon, I went to Tetem art space to have a quiet look at Walk-in Worlds. I watched the following three Virtual Reality 360° movies: Celebrating the Holy Object: You, Passing Down Poetry, and The Big Dance. The first one was recorded in Rijksmuseum Twenthe in the exhibition Ars Longa, which I visited last year. Next, I went to bookshop Broekhuis. On the top floor, I watched the exhibition with works by Simone Zacharias. I had seen this before briefly. I was intriged by the work Paarse Dag 2 and consider to buy it. At 16:40:50, I bought the following two books:
  • Ready Player One written by Ernest Cline in English and published by Random House in 2018, ISBN:9780525574347, for € 5.00.
  • The Stanley Kubrick Archives edited by Alison Castle, written in English and published by Taschen in 2016, ISBN:9783836555821, for € 11.95.


Friday, February 1, 2019


At 17:58, I bought the book Eindexamenwerk 1983 written by Sipke Huisman in Dutch and published by Akademie voor beeldende kunst AKI in 1983 from charity shop Het Goed for € 1.50.

Thursday, January 31, 2019

Artist talk Laurence Malstaf

This evening, I went to the artist talk by Lawrence Malstaf and the opening of the exhibition Double Compass at Tetem art space. Just right befor the talk, I was invited to try one of the Compass devices. It was an interesting experience, but a little too intrusive for me. I also did not understand the meaning until after the talk, and than thought about a simpler device to implement the same idea.

Before the start of the talk he showed a loop of a short clip from a movie. He told that he wanted to go to an art academy, but his parents wanted him to do something more practical, thus he went into industrial design, which in the end, he thought was a better choice, because he discovered that he likes to work with industrial materials rather than with paint. He showed clip of Der Lauf der Dinge from 1987, an industrial Rube Goldberg machine, which, to him, is like a theather of things. Next he talked about some of his projects. He started as a volunteer at a theater, but got more and more involded in theater and dance. This also raised his interest in the human body. People are attracted by motion. If there is a dancer in the room, people will follow him. If there is some video documentary besides a work of art, people will look at the video instead of at the work. Hs project Shrink (1995) is about putting people in vacuum bags. It about putting people in a stricted environment. This idea also returns in Compass. The question is whether you adapt to the environment or whether you resist it. The project Nemo Observatorium 2002 only gets meaning when you get inside it. Transporter (2008) invites you to become part of the project by laying down on it. Nevel is about a shape changing labyrith, where vistors become actors for the visitors that arrive after you. He show a slide with four themes in his projects. These are:

  • Being in the middle
  • Exhibitioning the visitor
  • performing objects and spaces.
  • presence and representation.
Being in the middle is also the title of his first exhibition. You are always in the middle of the complex reality that we are in. There is no way to escape it, to look at it from the outside. As an artist you also experience this when working on a project. Working on a project is like a scientific research project. It is a process. He said that art is about representing the reality. For him his projects are very abstract. Things that are not taken from reality, but have their own reality. It is something that happens, which you cannot control. He showed clips of Tollen projects (2016 and 2017) explaining that it does not feel really ready as a project. Pavilion (2011) is about flags filling a space. The sound that the flags made was something he had not anticipated and made it an interesting aspect. The flagpoles were controlled by a computer and although both arms moved synchrone, the movement of the flags was visually different and unpredictable. He also began to focus on minimalizing the materials used in his projects. An example of this is Event Horizon (2015), which just makes use of dust and light. The Compass project is the negative of the Nevel project: to make you feel walls that are not there. Utopia (2018) is not finished yet. It is part of a performance. It is about the nature of the future. Polygon is another project with minimal materials. Solid state (2012) is about a vibrating table. Tipping point (2013) is about water and some air moving between two glass plates. The first version was made from real glass. A second version used a (much lighter) transparent polymer. Conversations (2012) is about chairs that move around, due to a vibrating motor installed under the seat. After the talk, he answered some questions.


Wednesday, January 30, 2019


This afternoon, around a quarter to four, it started to snow. At first the snow did not stay. I had to bike how through the snow, which took longer than normal. When I arrived home, just before seven, I measured a little more than 3 cm of snow on table in the back garden. But there were still some spots on the ground that were not covered. More snow is expected to fall this evening and night.

Saturday, January 26, 2019


Yesterday afternoon, I saw some big snow flakes, but because the temperature was rising, it looked like the snow did not stay, expect maybe on the patches of snow that were left from Wednesday. In the evening it started to rain and this morning all the snow was gone (except for some very small spots where people had piled up snow).

At 13:37:45, I bought the book aki akademie voor beeldende kunst 1998-1999 (actually, a schoolyear diary for students) edited by Sipke Huisman, Bas Könning, and Regina Kroeders, with illustrations by Joost Roelofsz and Sipke Huismand, written in Dutch and published by AKI in 1998, from charity shop Het Goed for € 0.95.


Friday, January 25, 2019


Thursday, January 24, 2019


Wednesday, January 23, 2019


This morning, I measured that there was 2 cm snow on the table outside. It looks like a little snow fell during the night. If you would divide the country in four from West to East, then most of the snow fell in the third quarter from the West, with largest amount being 10 cm.


This afternoon, I went to bookshop Broekhuis. I first looked with the second hand books and the cheap English books at the second floor. Then I had a last look at the 50%-off sale at the ground floor, not expecting anything. But to my surprise, I found a little book with polaroids by the Dutch artist Aat Veldhoen. At 17:53:38, I bought the book Aat Veldhoen, polaroids edited by Ed de Heer written in English, translated from Dutch by Lynne Richards, published by Lecturis in May 2015, ISBN:9789462261235, for € 9.75.

Rubber straps

Continuing from yesterday, I wondered what would be the shortest sequence where all the combinations occur the same number of times in the sequence. I had some how hoped that this would result in a long sequence with interesting properties, however, it turned out to be rather boring, there is a unique sequence with length 20 where all the combinations are at least eight days apart:



Tuesday, January 22, 2019


At the end of the afternoon, it started to snow. The snow started in the West of the country and slowly moved to the East. This resulted in a record of 2287 Km of traffic jams, mostly people driving slowly. It is probably mostly a sign that people are no longer used to snow. Less of 1 cm of snow has fallen around here and it is even not staying at all places. I have not seen any real snow flakes yet. This morning, there was still some snow left from last Friday, especially at places that did not get much sun light.

Rubber straps

In the past days, I have been thinking about the colour rubber straps sequences. In the sequence that I am using now, it there are combinations that repeat after six days. I wondered if there are also sequences where all combinations occur only after seven or more days. Yesterday evening, I already found some solution to the problem. First of all, it is interesing to note the length of cycles that can occur in the Peterson graph are limited to: 2, 5, 6, 8, and 9. It is easy to see that the shortest sequence where a combination appears after two days, is equal to the shortest sequence that contains each combination at least once. It is impossible to create a sequence where each combination appears after then or more days. One can also easily see that a sequence where each combination appears after nine days, cannot contain all combinations. By combining a cycle of length eight and a cycle of length nine, you can create a cycle of length 17 where all combinations appear after eight or more days. I also found a shortest sequence of length twelve where each combination occurs after five or more days. And because twelve is one more than eleven, I presumed that it must also be the shortest. I did not find a shortest sequence where each combination occurs after six or more days. I played with the program I used before and after some time, came up with following results:


These match with the solutions I had already found and gave a solution for the last unsolved sequence.

Monday, January 21, 2019


February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
Alzheimer's Disease
Trip to China 2010
-- contact --




Art works
Useless lists


My life as a hacker
Signature programs
Software enginering
The Art of Programming
eXtreme Programming Programs


Hamilton cycles
cutting sticks
Califlower fractal


Volcano Blog


The email address below, may only be used for private communications. This email address may not be put on any mailing list. I do not want to receive emails with advertisements of any kind. My email address is:

Privacy statement

This is a static website with no contact form and no way to add comments. It has no advertisements and no trackers. It does not use cookies. I am not using any method to analyse traffic to this website nor keeping any logs. I am not collecting personal data besides what is published on this website. If you want me to remove any personal data (including your name or link to your website), please contact me by above email address and I will make all effort to remove the data as soon as possible. I am private person and this website does not serve any economic purpose. All cost for maintenance are paid by myself. I do not receive any payments. The website is ad-free and does not have sponsored links.

Site statistics

If I did not count wrong, this site consists of 962 HTML-files with a total size of 22,259,783 characters, having 46,845 internal links and 10,586 external links to (more than) 3,578 websites. (At least 731 of the external links are broken.) Furthermore, it contains 206 C/C++ program files with a total size of 4,643,602 characters, and 3 PASCAL program files with a total size of 35,259 characters. There are 73 text files with a total size of 774,699 characters. With respect to images, this site containts 1241 JPEG images (total size 54,154,778 bytes), 146 GIF images (total size 3,765,046 bytes), 92 PNG images (total size 2,253,317 bytes), and 2 BMP images (total size 3,727 bytes). With respect to sounds, it contains 14 WAV files with a total size of 389,002 bytes and 1 MP3 files with a total size of 70,182 bytes. It also contains 43 PostScript files (total size 308,387 bytes), 2 LaTeX files (total size 132,020 characters), 8 PDF files (total size 640,573 characters), 22 zip files (total size 2,487,335 bytes), 3 gzipped tar files (total size 52,345 bytes), 45 SGF files with a total size of 85,019 bytes, 103 KML files with a total size of 4,332,209 bytes, and 2 EXE files with a total size of 38,340 bytes. It also uses 15 JavaScript files with a total size of 650,266 bytes, This leads to a total size of 100,449,631 bytes.


Creative Commons License

I, Frans hold the copyrights of this and all other pages on this website. For this website a Creative Commons License is applicable. You may not use this work for commercial purposes. I consider all computer programs to be copyrighted by me under the GNU General Public License, unless stated explicitly otherwise. All quotes (text and program fragments) from other sources are excluded from this, and should be considered as copyrighted by their authors.

(This space is intentionially left empty)