Note

The ancestor filter has been deprecated. Use

  X≺Y

instead of

  ancestor(X Y)

ancestor (deprecated)

The ancestor filter takes two positions as arguments enclosed in parentheses. It matches the position if the first position is an ancestor of the second position:

   ancestor(x y)

We say that position x is an ancestor of position y if, starting from position x there is a nonempty sequence of moves from the PGN file that reach position y.

If x and y are mainline positions, then x is an ancestor of y if and only if the position id of x is smaller than the position id of y. Thus, in this case, one can test if x is an ancestor of y simply by doing:

  x<y

Note that ancestor (x y) is equivalent to descendant (y x) .