Part I ABOUT DDT PUZZLES

Although DDT puzzles are just another variant of Classic Sudoku puzzles, this was not the motivation behind their creation. This may seem odd, given the view widely adopted by publishing companies that new puzzle types are needed in order to maintain, and potentially broaden, the popularity of Sudoku. In my humble opinion (), in the past, most puzzle constructors have focused on creating increasingly harder puzzles, rather than attempting to develop universal solving methods that would make puzzle solving easier and more enjoyable to broader audiences.
This is attested by a comment a publishing agent recently made in conversation, claiming that she always spends her time on a plane solving Sudoku puzzles, yet she has never manages to complete even a single one during the flight. My observation seems to be true (). What is needed is a magic wand to transform an ordinary book into a Sudoku manual that would provides universal methods and techniques that could be used to solve any puzzle, even the hardest ones.
As there are no magic wands on the market, though books on Sudoku abound (), the times when people will be able to leave the plane satisfied and happy that they have solved a difficult Sudoku puzzle still seem far away ().In fact, it seems unlikely ordinary people will be able to experience the satisfaction of solving hard Sudoku puzzles anytime soon.. Thus, it is my hope my book, “Mystery of Sudoku,” will soon be published. Mystery of Sudoku allows all Sudoku lovers to enjoy solving a wide range of puzzles-even the hardest ones.
It is now clear why I never intended to create a new type of Sudoku puzzle although I worry my reasons for creating DDT puzzles may leave an impression of a less than modest man (). In writing Mystery of Sudoku I had an idea about creating an exceptionally hard puzzle, which preoccupied me such that I stopped writing in order to focus on my creation. The result of this endeavor is a wide range of DDT puzzles, some of which will be included in this collection.




When I read what I have written above I am rather satisfied with myself. However, a nagging thought comes to me - what if readers do not believe that I am capable of constructing exceptionally hard puzzles? In order to allay my worries and satisfy the curiosity of more skeptical readers, I have made the decision to include the hardest puzzle I have ever created (). As I am sure many readers will attempt to solve this puzzle, I would like to stress this is not a typical DDT puzzle, which makes finding the correct solution even harder. Moreover, if the GIVEN NUMBERs in the first, fifth and ninth box were omitted, this would be virtually impossible as shown in Fig A. Finally, once I created various versions of DDT puzzles, I resumed writing my book. Still, from time to time, I would go back to my hardest puzzle and enjoy retracing my steps towards the solution (). Although I was aware that it was not “AI Escargot” and was unlikely to be published in the world media I took pleasure in the mental challenge it posed even to me, the creator. After a while, I realized that there was a way that the puzzle could be made even harder—by modifying its ”gene” in the FIELD 83, as shown in Fig B. The name “gene” is indeed appropriate, as it defines the puzzle properties. What is even more interesting is that, to me, it all started to look like a “gene”—different apparitions come to different people, and I am no exception (). Some see “fish” in Sudoku, and I see “genes.”Moreover, the concept of “gene” has other implications, as now that the puzzle “mutated,” it may seem that it is impossible to solve. This was, in fact, confirmed by a number of Sudoku lovers I sent the puzzle to without providing any additional explanations. However, creating such structures is only possible in DDT puzzles, as classic Sudoku puzzles have no “genes” (). The proof that this puzzle, shown in Fig C, with “modified gene” has a single solution can be found through the DDT puzzle solving methods, which is yet another challenge for the readers of this collection.