file filter is a numeric filter that takes a single set filter as argument:
file a1 ≡ 1 file c3 ≡ 3
If the set of squares represented by its argument contains a single square s, then the value of the
file filter is the numeric value of the file of s. The numeric value of the files are 1 for
a; 2 for
b; and so on up to 8 for
If the set of squares represented by its argument does not contain exactly one square, then the
file filter does not match the current position.
file filter is not affected by transform filters, such as
file filter is used in averagedistance.cql, chameleon.cql, flipverticalecho.cql, horizontallysymmetric.cql, platzwechselecho.cql, platzwechseln2.cql.