Depth in Bingo Closure
  Bingo is played on a $5\times 5$ grid. Take the 25 squares to be the ground set of a closure system in which square $s$ is dependent on a set $S$ of squares iff $s$ completes a line - a row, column, or diagonal - with squares that are already in $S$. The closure of a set $S$ is obtained via an iterative process in which, at each stage, the squares dependent upon the current state are added. In this paper we establish for the $n \times n$ Bingo board the maximum number of steps required in this closure process. 
Jeffrey Beyerl, J. Bowman Light, Robert E. Jamison
math.CO