He has developed what he describes as a percolation model for word puzzles. In his paper, Hartmann writes that he came to the idea of a percolation model for word puzzles while working on one himself.

According to his paper published in the journal Physical Review E, the crossword puzzle-solving process resembles a type of phase transition known as percolation—one that seems to be unique ...

According to one physicist, the answer is simple: Percolation. “When a statistical physicist looks at a partially solved crossword puzzle, she or he sees immediately a percolation problem ...