About Sysudoku

Systematic Sudoku (Sysudoku) is about human engineered techniques for solving Sudoku puzzles of all levels.

The most distinctive feature of Sysudoku is the active solving nature of the candidate gathering phase, Sysudoku Basic.

Instead of immediately deriving all possible candidates from given clues, as most Sudoku writing assumes, Sysudoku Basic uses clues, subsets, and unmarked strong links on an uncluttered grid to find clues and subsets.

The first Basic stage is called the bypass because, although it uses slinks in solving operations,  it bypasses the pencil marking of slink candidates, except for those in subsets.

Like a clue, a subset bans candidates of its values elsewhere in its box or line.  The idea is to work on a grid, clear of candidates except for those reserving cells.

Drag off About Sysudoku  on the Menu Bar and click on Bypass & Tracing for a detailed illustration of the bypass on a Washington Post Saturday 6-star, then return here to continue the description of Sysudoku Basic.

The second stage of Sysudoku Basic, box marking,  records box slinks, the strong links defined by boxes.  

Instead of a linear or keypad style of positioning candidates within cells, Sysduoku uses pencil mark positions to mark slinks and subsets. The two candidates of a box slink see each other in matching positions at the top of two cells of the box. Row slink members are in lower left corners of two cells on the row; column slink members, in lower right corners of two cells of the column.  There’s also a place for members of aligned row and column triples.

Absent a traced follow up of clues found in box marking, the trace can be short and simple. It only lists the boxes containing slinks and aligned triples of each value. Here’s the trace for the bypass example 6-star.

The box marked grid shows the cell positioning of box slinks. In addition, there is one aligned triple, which may later affect the placements in the SW box. It was created by the 1-clue at r5c3.

Line slinks, the strong links defined by exactly two candidates of a value in the line, are marked in a third stage (line marking), along with all remaining candidates.

Lines are filled efficiently by posting a fill string, a string of missing values, at the end of the line, and making a copy for each cell to be filled, removing from the copy each clue or line slink value seeing the cell being filled, and finally, adjusting the cell position of candidates to reflect new line or box slinks, and marking new bv cells.  Lines are filled, fewest unfilled cells first. When lines in one direction are all filled, so are lines in the other direction, but line slinks remain to be marked in the unmarked lines.

For the line marking solution of the Washington Post 6-star, click Line Marking Solution off About Sysudoku, then return here.

Sysudoku Basic, with its strong link and bv marking, combines basic solving while  preparing the grid Sysudoku Advanced, a systematic progression of increasingly difficult methods, starting with more easily spotted elimination techniques. Its most distinctive features are:

  • Medusa coloring networks of strong links,  
  • sets of practical ALS and pattern analysis techniques, and
  • a fully armed version of AIC building.

For graphic demonstrations and preview explanations, click About Advanced, off  About Sysudoku.

Most of the posts report solution paths  of difficult puzzles as a way of rating published collections or reviewing Sudoku authors. Explanations in the posts are backed up by the Guide. Illustrated examples are taken from very limited sample puzzles selected from collection reviews and instructive books and sites, and newspapers, under “fair use” guidelines.

Sysudoku is free of ads and subscription fees, and offers free ©PowerPoint and ©Word templates for the puzzle grid, and for basic and advanced techniques seen in the posts, by email attachment, upon request to the address below. The Guide will be eventually be published in book form, for reading offline.

Sysudoku is no longer posted weekly, but continues with updates and new posts as announced on a final post serving as home page. The site is supported by ©WordPress, with the Twenty Ten style theme.

Comments are welcome and appreciated, though only those about the subject of a relevant post are published. Except for the most recent, comments appear only on the post addressed, so make your comment on that post. If it’s about the blog in general, this About Sysudoku page is the best place to comment.

Sudent is my blog name. I’m John, at jamwelch64@email.com.


26 Responses to About Sysudoku

  1. Natalie / Sophie says:

    hi we looked up your website as soon as we heard about it (we’re your naybors) we thought it looked cool and that you designed it very nicely

    • Sudent says:

      Natalie and Sophie, thanks for your generous comment. I know you are learning about good writing as a way to communicate your ideas, and I will not be surprised to be reading your blogs before long.

  2. Ali says:

    yes, yes, yes…NEVER GIVE UP!!! Congrats on finding life lessons through your game…I’ve never been able to do Sudoko…just not enough brain power I guess, lol.

    • Sudent says:

      Thanks, Ali. Believe me, it would be fascinating to discover how far you can go. It has been that way for me. All you need is a proper beginning. And its here.

  3. I truly enjoy examining on this internet site , it holds superb posts . “Dream no small dreams. They have no power to stir the souls of men.” by Victor Hugo.

  4. Agen IBCbet says:

    I do trust all the ideas you’ve presented to your post. They’re really convincing and can certainly work. Still, the posts are too brief for beginners. May just you please lengthen them a bit from next time? Thanks for the post.

    • Sudent says:

      Sorry, Lessley. I cannot make the current posts self contained. I think that is what you really want. I try to limit posts to one significant, but advanced idea. To make use of them, you must scan the pages and start with beginning posts and work forward. But don’t despair. It’s more interesting back there, because the earliest stuff applies to all Sudoku puzzles.

  5. richardgoodrich says:

    I have enjoyed your systematic sudoku more than any other. I am long over due saying so! I just bought Denis Berthier’s “The Hidden Logic of Sudoku” and have been trying to write a Visual Studio 2008 C# program that combines some of his ideas and yours. The biggest breakthrough for me has been your “slink” marking. I am trying to build a user interface that would allow a place to mark block slinks, row slinks, and column slinks with the “pencil marks” in the center. I got distracted by Wen Pei’s book of solving Sudoku in visual basic. I was in the process of converting his code to C#, when “work” raised its ugly head and demanded most of my time back. I have some different ideas on trace and have developed some of my own ideas – but not as complete as yours! I am an electronics engineer in a small company and a “hack programmer” My wife is concerned with my new addiction – actually a restored addiction at a much higher level then before! Sadly, it seems sudopedia.org has disappeared, so finally decided I should respond and thank your for your site. We aren’t getting any younger!

    Richard Goodrich

    • Sudent says:

      Richard, you made my day! Comments that reveal comprehension of my work are rare. I will respond to your trace comment as time allows, perhaps acknowledging it in a post.

      Before the blog, I wrote out about 2000 lines of Java code on basic solving, but abandoned the project when I realized that my programs data resources had already far exceeded ordinary human capabilities. You can appreciate how this pulled me back into visual aids and theoretical explanations of the “human engineered” theme. I want to follow your successes in dealing with Berthier’s “resolution methods”. My own encounters are reflected in “Berthier’s xyt-chains” of 12/27/11, “Casting for Regular Fish” of 4/3/12 and Berthier’s ‘useless’ claim in “XY Loops” of 3/16/12.

  6. high pr list says:

    Hey there! I was curious to know if setting up a blogging site such your own is tough to do for inexperienced people? I have been wanting to create my own blog for a while now but have been turned off because I’ve always believed it demanded tons of work. What do you think? Bless you

    • Sudent says:

      Look up WordPress. They offer domain management, data space, and an interface that makes blogging easy. The hardest part is deciding what options you need. I started out simple, and remain that way. Dumb and happy.

  7. Maija Ingelin says:

    I am a great friend of Krazydad Insane sudokus. Still, I´m no strategist. Would like to learn to master some strategies if they could lessen my futile work. (But I have been lazy to learn them).

    Would have one question, to begin with:.
    Krazydad informs that their Insane sudokus can´t be solved without at least one guess.
    My experience is that that is true.
    If my first guess is a ´stupid guess´, (i.e.a haphazard guess), is it so that solution necessarily requires many many new guesses,.
    But if my first guess is a ´good guess´, does it lead to the solution quicklier, with fewer guesses.
    Have you an opinion if this?
    Yours faithfully, Maija a macska

    (or maybe no further guesses at all). I have experience of both.

    • Sudent says:

      Thanks, Maija, for reading and for your question. By “haphazard”, I take it you mean without a logical reason. I agree with you that such a guess is stupid. Even if it leads to a solution, that solution is all you have gained, and that was there all along, in the back of the book. So what is a good guess? I call it a trial. A trial is a timely and intelligent guess. It is anything but haphazard. It is assembled logically, and will gain information for further solving regardless of its outcome.

      Trials are not “trial-and error”. The “error” in trial-and-error” is making a guess which, if it fails, tells you nothing.

      Trials are to be made when no further direct logical inferences can be made. That way, the trial outcome cannot obscure logical contradictions in the puzzle that you might have discovered. As you learn more, you might go back to puzzles solved by trial, and attempt to bypass them.

      Finally, yes. Trials take bigger steps and come in much shorter sequences. Computers do back tracking well but humans don’t. The posts of the Insane review are a good introduction to trials. They show conclusively that many Insanes can be solved by direct logical inference without trials, and certainly without haphazard guesses.

      • Maija Ingelin says:

        Thank you very much for your valuable answer to my question. Very good indeed.

        I now literally understand what a Trial is.
        Krazydad´s 9×9 Insanes, so the producer says, CANNOT be solved without at least one guess, that is: one trial. In my experience, that is true.
        (Valuable information right at the start, because it tells you it´s no use trying to solve them by mire direct logical inference. Saves futile work.)

        You mentioned ´posts of the Insane review´, which are ´a good introduction to trials´ .
        I didn´t understand what that meant. Is it perhaps a book that you can buy?
        On the other hand I no longer really need such a helpful book. My own solutions teach me all the time, and it´s real fine to see.

        Happy sudoku future, Maija a macska

      • Sudent says:

        Hi Maija,

        “Posts of the Insane review” are the posts of this blog that cover the solving of the 10 Insane puzzles selected for the review. If you give up Sudoku books, I hope you will continue reading Systematic Sudoku. If I get a book out, it will be to present the lessons of the blog more clearly and efficiently than is possible in a blog.


  8. Maija-S. Ingelin says:

    Hello John,
    I have written you earlier as I am a great friend of Krazydad´s Insane Sudokus.
    Got good answers from you, thank you.
    Would have one more question. I hope I can formulate the question understandably enough.

    Have noticed long ago that when I make so called guesses (or trials), their number varies greatly.
    Sometimes this depends on my own lack of ability, but sometimes it depends on the sudoku (some of them are easier, some are harder)
    My question is: Take one particular insane sudoku. Is there A DEFINITE MINIMUM NUMBER of trials which are needed?
    Supposing that minimum number is four, and I need, say, nine.. That then means my five extra trials arise from my own mistakes, and the problem is to find the minimum number, four.
    And it is useless to try to solve the sudoku with LESS THAN FOUR trials.

    Kind regards, Maija a macska.

    • Maija-S. Ingelin says:

      “Awaiting moderation”? Was there something wrong with my comment, or what does “awaiting moderation” mean?

      • Sudent says:

        Hi Maija,

        “Waiting moderations” is a message that you are on the blog’s approved list, and that I am notified by email that your message needs attention. Congratulations! All messages to WordPress are reviewed by the blog moderator (me, in this case) before being published.

    • Sudent says:

      Maija, that’s a pretty deep question you have. I’m not a puzzle composer, but I can tell you there is no minimum number of trials, because there are so many possible trials and it is impossible to anticipate them. The harder the puzzle, the longer the trials and the more chance that they will be indecisive. This is because the puzzle has more “almost” solutions. Its more slippery. I strive for fewer trials by making each trial involve many candidates. Also, I use trials when there is no foothold for logical discoveries. Thanks for your question.

    • Maija-S. Ingelin says:

      Thanks very much for your reply regarding minimum number.of trials required.
      The main point in your answer is that THERE IS NO MINIMUM NUMBER. That is precisely what I wanted to know. It makes a great difference if I know that no minimum number exists. Maija a macska

  9. Hello John. I love your book “Mensa’s Guide to Solving Sudoku” by Peter Gordon. It is through this website I know your real name. Based on the strategies in your book, I recently published a book “CREATE CLASSIC SUDOKU: Make Your Own in Minutes” on Amazon.com.

    I really appreciate of your “Mensa’s Guide to Solving Sudoku”, which guides me writing a computer software program to generate Sudoku puzzles in minutes and later ideas to handcraft your own Sudoku puzzles. Please let me know whether you are interested to have copies of my book. I would love to give you 1-3 free copies if you want to. My email address is hello@createclassicsudoku.com

    Wish you a great long weekend!

    Most respectfully,

    • Sudent says:


      How could you get it so wrong? Elsewhere on my blog, you will find that I reviewed Peter Gordon’s Mensa Guide, and not favorably. If your book were based on strategies of my blog, I would be interested in your book, but if it is based on the Mensa Guide, please don’t send me a copy.

  10. I have developed a new sudoku puzzle game “Sudoku Octangles” for iPads and iPhones:

    I hope you like

  11. solvayblue says:

    I’ve posed this question to a number of columnists including Marilyn vosSavant but can’t get an answer. I apologise if this is available elsewhere. Can you tell me what the bare minimum number of cells in a sudoku grid is sufficient to generate a unique solution? Usually difficult ranked puzzles have about 24 or 25 supplied values but I suspect the minimum is something fewer.

    • Sudent says:

      The generally accepted minimum is 17, and some collections treat being at this minimum as a feature. However, it is also accepted that number of clues is not well correlated with difficulty. In fact some have observed that minimum puzzles seem to be a bit easier. Marilyn has her own number placement thing in puzzle world, unrelated to Sudoku. Hpe this helps.

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