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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.

Saturday, March 23, 2019

Learning Chinese

Because we have plans to make a trip to China this year, I have decided to learn some Chinese. I have installed the ChineseSkill Android app and finished some of the basic lessons, but since this morning, I get a message that I am out of pandas and I have no idea how to get more. Maybe because I have no payment method installed. Maybe I have to take a look at some other Android apps. I am also thinking about making my own flashcards and go over them when I bike to my office or listen to language learning mp3's. I found the video 200 Chinese Phrases for Beginners from the Learn Chinese 360 YouTube channel, which seems to be an interesting starting point to improving listening. This morning, I also started reading the Dutch book Het karakter van China (known in English under the title China: Empire Of Living Symbols) by Cecilia Lindqvist, which might be a good way to learn Chinese characters.

One flower

At the end of the afternoon, one flower of our magnolia had opened a little. Expect that many more flowers will open in the coming days.


Early this evening, I bought the drawing Bikerider from Maria Britze after her exhibition Colourtramp at B93 came to an end today.

Wednesday, March 20, 2019


Yesterday evening, I made some modification to my Exact Cover program, such that it can be used to estimate the number of solutions of the Octopuszle. This morning, I made some modifications of the program. The idea of the 'sample' mode is that it will run for two minutes using a random selection of vectors from the column with a minimum value of vectors. While doing so, it measures the distance of the solutions spaces that has been covered under the assumption that each selection covers an equal part of the solution space. It also counts the number of solutions that were found. These two can be used to estimate the total number of solutions. However, the assumption is not correct and does influence the result. This morning, while biking to my office, I realized that there is an easy way to estimate an upper limit on the estimation. There are 256! ways of putting the pieces within the 16 by 16 square. Now, what is the chance that all pieces fit. There are a total of 2.(2.162-16.15) + 2.(2.162-152) relationships that have to meet. If we assume that all the chances are independent, which is probably not the case, than the number of solutions are about 2.409128076060726988778E+170 (found by calculating the expression 256!/(2^(2*(2*16*16-15*16)+2*(2*16*16-15*15))) with Keisan Online Calculator. I have no idea which statisical method I should use to look at the numbers produced by the sample mode, but if I just have a look at the numbers, it seems to return a number around 10163 solutions. This is close to the theoretical maximum number of solutions.

Saturday, March 16, 2019

Exhibitions and book

I went to XPO to see the exhibition A Blue, A Purple, Aloë vera, Aster, Banaan, Cupcake, Engeland, Hibiscus, Pilli Pilli, Prinsessen Roze, Selectie and Ultiem by Evangeline Clark. She was there herself and I talked a little with her. I think about buying Pilli Pilli. Next, I went to bookshop Broekhuis, where at 16:08:40, I bought the book De edele kunst van not giving a fuck written by Mark Manson, translated from the English The Subtle Art of Not Giving a F*ck into Dutch by Annoesjka Oostindiër and Henk Popken, published by Bruna Uitgevers in 2017, ISBN:9789400509023, for € 20.99. I walked through the city and went to have a look at the exhibition Monsterproject at Concordia. In a bookshelve, I discovered a copy of Jaarboek 09/10. I made some inquiries as to if it was on sale, but it was not. I did get some tip about another place where the AKI yearbooks can be found.

Octopuszle solutions

A large part of the day, I worked on a program to generate an exact cover problem for solving The China Labyrinth within a more compact, hexagon shaped, enclosure. As usual, a one off error, was the last bug that kept the program from running. Below one of the solutions is given.

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I noticed how this solution consists of three parts (counting the empty piece as a separate part), and it only has one loop (circling the empty piece), which seems to be a counter example of the statement that I quoted yesterday. Maybe the proof is not as solid as it was thought. Because there are so many solutions to the puzzle, I thought that maybe an algorithm that would search for solutions at random would give a more varied number of solutions. When I started working on this, I discovered a bug in the algorithm, that was introduced when I did some experimentations on reducing while solving. When I fixed it, the program returned many solutions per second. I decided to also give it a try at Octopuszle and for that too it produced many more solutions than before. Below ten random solutions are given.

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Friday, March 15, 2019

The China Labyrith

While thinking about better ways to solve the Octopuszle, I decided to take one of the diagonals away, and try to fit the 64 remaining pieces into a 8 by 8 grid. Even then, the program did not find many solutions per hour. I let the program run some time until it found 1900 solutions. I did think about some ideas to find more solutions. I did realize that the remaining puzzle was actually The China Labyrith inside a rhombus. After realizing this and remembering the statement: "It was soon discovered and proven that the number of seperate groups (the blank counting as one group) will always equal the number of loops (holes in the solution)", it became clear to me that one of my approaches to find more solutions, was never going to work. Also it is clear that the one piece with no lines, cannot be at the edge, but must always be in the middle. This evening, I worked at the visualization of one of the solutions, also to verify that my mapping to an exact cover was actually correct. The visualization uses one of the lines generated by the exact cover algorithm.

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Saturday, March 9, 2019


At 15:58, I bought the book Science * Art written by Ans van Berkum and Tom Blekkenhorst in English and published by The Fentener van Vlissingen Fund, ISBN:9789090013596, from charity shop Het Goed for € 2.50.

Magnolia seed

This morning, I noticed that some of the outer shells of the flowers of our magnolia had cracked, a sign that it might start flowering within some weeks, which would be rather early this year. I decided to have a look at the one seed that I had discovered last year and kept in our shed, only to discover that it was covered with mold. In the afternoon, told Annabel about. She went to inspect the magnolia and discovered two other withered pods that had contain one or two seeds. Annabel noticed that it is not so difficult to grow a magnolia from a cutting. I told her, that I rather grow one from a seed. This fall, I will look more carefull for seeds and hopefully treat them better.

Friday, March 8, 2019


Wednesday, March 6, 2019


I went to the opening of the exhibition Colourtramp by Maria Britze at B93. I found her newest work, drawings made with colour pencils, the most interesting, and I was not the only one in that regard. I want to buy one of these drawings.


  • Ghidra: A software reverse engineering (SRE) suite of tools developed by NSA's Research Directorate in support of the Cybersecurity mission

Monday, March 3, 2019

Paarse Dag 2

This evening, I went to collect the art work Paarse Dag 2 made by Simone Zacharias, which I had first seen on Saturday, February 2. Again, a work with both figurative and abstract elements, just like most of the other works that I bought in recent years. It seems that purely abstract is too abstract for me. I also like the colours in this work, as purple ('Paars' in Dutch) is my favourite colour.


Saturday, March 2, 2019

The naked truth

In the afternoon, I went to Rijksmuseum Twenthe for the exhibition De Naakte Waarheid (The Naked Truth. I found the following works notable (in the order I saw them):
  • Digital artifacts 2014 by Bart Hess
  • Adam en Eva 1914-16 by Jan Sluijters
  • Fallen Angel 2011 by Christiaan Zwanikken
  • De Prediker (zelfportret) 1937 by Carel Willink
  • Het slachtoffer van de ellende 1892 by Marie de Roode-Heijermans
  • Body Builder (Profile) 1976-1978 by Andy Warhol (four photographs sewed together)
  • 4 nudes 1889-1915 by George Hendrik Breitner
  • 023. Dreads 1998, 066. Babes 2005, and 156. Good Morning 2018 by Ellie Uyttenbroek and Ari Versluis
  • Halfnaakt (vrouw van de schilder) about 1912 by Jan Sluijters
  • Halfnaakt 1964 by Aat Veldhoen
  • Paring 1962 by Aat Veldhoen
  • Selfmade: Duisternis (3) Heleen van Royen
  • PSP Ontwapened by George Noordanus and Hendrik Jan Koldeweij
  • Phil Bloom with newspaper, fragment from HOEPLA, episode 2.
  • A History of Sex (Rietveld) 1996 by Andres Serrano
  • A History of Sex (Eline) 1996 by Andres Serrano
  • A History of Sex (Leo's Fantasy) 1996 by Andres Serrano
  • Chair 1969 by Allen Jores
  • The Palace of Automorphic Delight 2009 by Terry Rodgers
  • Veneration (The Chapel) 2017 by Levi van Veluw
  • Study for Racional 2004-2007 by Yoan Capote
  • Easy to remember 2011 by Lorna Simpson
  • Blue 2016 by Ingrid Baars
  • Mother and Child 2008 by Luo Fahui
  • Falaises près de Pourville 1882 by Claude Monet
  • Freeing (the body) by Marina Abramović
  • Untitled (C.M. #10) 2015 by Juul Kraijer
  • Untitled (L.P. #7) 2015 by Juul Kraijer
  • Paring 1962 by Aat Veldhoen
  • Copulation 1961 by Aat Veldhoen
  • Zonder titel/Untitled (4x) 2015 by L.A. Raeven
  • 10 meters of sound by Philip Vermeulen

Afterwards, I went into the city. At bookshop Broekhuis there was an exhibition with works by Jeanine Wubbels. I also went to photo gallary Objektief to see the exhibition MALE. HAIR. -3 by Rem van den Bosch.

Tuesday, February 26, 2019

Hexagon numbers

This afternoon, I thought about the hexagon numbers not with triangles but with hexagons on the corners of the triangles. That is because I wanted to know if there is a hexagon with 64 smaller hexagons. If every side should have more than one hexagon, the smallest configuration you can create, consists of seven hexagon. The following sizes, above seven, are not possible: 8, 9, 11, 15, and 17. There are several ways to make a hexagon with 64 hexagons and the most round shape seems to have sides of lengths going round: four, seven, four, fife, six and five.

19.2° Celcius

This morning, between seven and eight, the temperature was still around -1° Celsius, but around four in afternoon, it reached 19.2° Celsius. Very likely a record, probably also for the whole month of February.


Saturday, February 23, 2019


Thursday, February 21, 2019

Alita: Battle Angel

Annabel and I went to see the movie Alita: Battle Angel. We both did not have high expectations of this movie, but we both enjoyed it very much hoping that a sequel will be made soon.

Wednesday, February 20, 2019


Tuesday, February 19, 2019

Octopuszle 4x4

Yesterday, I got an idea for finding solutions for the Octopuszle. The idea is to split the large puzzle in four by four smaller puzzles. If you look at only the horizontal and vertical lines, then there are 652 solutions of all possible pieces within four by four pieces. I discovered that there are no solutions when you only look at the diagonal lines. This night, I ran the Exact Cover solver to figure out how many solutions there are for filling a four by four square with all of the pieces, such that there is exactly all the pieces are used when ignoring the diagonals. The answer was 170,917,888. Today, while biking, I concluded that there might not by any solution at all, simply because of the pieces that are needed at the border. Not suprisingly, 170,917,888 is equal to 652 times two to the power 18. I have no idea how to proceed from here.

Saturday, February 16, 2019

Come together in a dream

I went to the opening of the exhibition Come together in a dream by Emmy Zwagers at XPO. I liked her work acryl op paper 300x400 2017. I understand that for her the process of making the work is as important as the result.

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


March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
Alzheimer's Disease
Trip to China 2019
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