The ply filter is a numeric filter whose value is the ply value of the current position. The ply value of the initial position is 0, and the ply value of any other position is one greater than the ply value of its parent.


The ply filter is used in averagedistance.cql where the filter

requires that the ply of the current position be greater than 10. The ply filter is also used there to compute the average move length: