The . character

The .-filter is a set filter that represents the 64 squares of the chessboard. It matches any position.

The .-filter can be used as a way to accept "any position" within a line filter:

    line --> .
         --> Ra3
matches a position where the white rook is on a3 following the current move.

As a set, the .-filter is useful where one explicitly wants to consider all squares.


The .-filter is used throughout the examples. One instance is
R. Becker, Olympia Dunyasi 2013
(found from CQL file: maxqueenattack.cql)

shows a position where the white queen attacks the maximum 27 squares. It was found from the cql file maxqueenattack.cql .