# Shikaku puzzle

The popular logic puzzle Shikaku has alternative English names: Divide into Squares and Divide into Cells.

They quite accurately convey the nature of the game: to win, you really need to divide the playing field into cells, taking into account the denomination of the numbers placed on it. The rules of this game are simple, but it is difficult to win, which is the peculiarity of most Japanese puzzles.

## Game history

The historical homeland of Shikaku is Japan, where this game is called Shikaku ni kire (四角に切れ). It was first published in Nikoli magazine, which began publishing a column dedicated to logic puzzles in the late 1980s.

Between 1989 and 1999, the magazine published hundreds of unique logic games, which were repeatedly remade, corrected, improved and renamed. The authorship of the ideas belongs to both Nikoli staff members and numerous readers who sent letters to the publishing house.

The founder of the magazine, Maki Kaji (鍜治真起), noted that one of the features of the published puzzles is a gradation in complexity: from the simplest (amateur) to the most complex (professional). For Japan, this approach is traditional: in this country, everyone must go a long way in the hierarchy from the very bottom to the top of the career ladder. Accordingly, increasing complexity in games (logical, computer) is also an invention of the Japanese.

It is noteworthy that the famous games published in the pages of Nikoli magazine and distributed throughout the world are almost always without authorship. Only the pseudonyms and gender of the readers who sent letters to the publishing house are known. According to statistics, approximately 80% of published game creators are men.

The only way to learn more about them is to attend the Nikoli party, held annually in Tokyo. It brings together both the magazine's staff and invited guests, including the authors of logic puzzles.

The game Shikaku is a rare case when it is not the author’s pseudonym that is known, but his real name. This is Yoshinao Anpuku (安福良直), a reader of Nikoli magazine who has immortalized his name in the history of Japanese puzzles. Although Shikaku was originally intended for purely entertainment purposes, today it is often used as a textbook for mathematics. So, in many schools they demonstrate the rules using her example:

- prime numbers;
- divisors;
- square roots;
- perfect squares;
- areas of rectangles;
- areas of squares.

For all its simplicity, Shikaku simultaneously demonstrates at least 6 mathematical concepts, namely the concepts of inclusion, disjunction, union, section, bijection and intersection. This puzzle is really valuable from a mathematical point of view, but only for those who are seriously involved in the exact sciences. For everyone else, Shikaku is just a great way to spend leisure time and practice your logical skills.

Try to play Shikaku once (for free and without registration), and you will never leave this game!