Nonuniversality for crossword puzzle percolation.

A percolation model inspired by crossword puzzle games is introduced. A game proceeds by solving words, which are segments of sites in a two-dimensional lattice. As a test case, the iid variant allows for independently occupying sites with letters, only the percolation criterion depends on the existence of solved words. For the game variant, inspired by real crossword puzzles, it becomes more likely to solve crossing words which share sites with the already solved words. In this way avalanches of solved words may occur. Both model variants exhibit a percolation transition as a function of the a priori site or word solving probability, respectively. The iid variant is in the universality class of standard two-dimensional percolation. The game variant exhibits a nonuniversal critical exponent ν of the correlation length. The actual value of ν depends on the function which controls how much solved words accelerate the solution of crossing words.