The History of Picture Sudoku
Picture Sudoku on small grids is a children's version of the number puzzle that became popular around the world in the mid-2000s.
From Latin Squares to Sudoku
A grid in which every symbol appears once in each row and each column is called a Latin square. The Swiss mathematician Leonhard Euler wrote about such squares in the 18th century.
The puzzle with boxes as well appeared in 1979 in an American puzzle magazine under the name Number Place; it was designed by Howard Garns. The Japanese publisher Nikoli took it up in 1984 and gave it the name Sudoku.
Small Grids and Pictures
After Sudoku became popular around the world in the mid-2000s, smaller versions with 4 x 4 and 6 x 6 cells and versions with pictures instead of digits appeared, especially for children: the rule is the same, but there is less to keep in mind at once.
How PaperGames Makes Each Puzzle
Every puzzle here comes from PaperGames's own generator. It fills a complete board at random, then takes animals away one by one - but only while the puzzle keeps exactly one solution and can still be solved with the two simplest steps: only one animal fits a cell, or an animal has only one cell left in a row, column or box.