This is a ProbLog variant of the nested number guessing example on http://forestdb.org/models/nested-guessing.html, illustrating nested queries using ProbLog’s subquery primitive. Two players a and b each randomly choose a number between 0 and 9, and they win if the numbers sum to 13. Player b observes a’s number before choosing, wrongly believes they win with any sum greater than 8, and conditions his choice on this knowledge. Player a in turn is aware of this, and takes it into account when choosing.