oah·2 anni fa·discussa2a3 on the first move or on the second move after e2e4 outputs that you have played an illegal move.But this is a bug as these are legal moves.
oah·2 anni fa·discussA sort isn’t necessary. Duplicates can be counted in linear time by using additional memory (e.g. with a hashmap)However, the point of the article still stands.
But this is a bug as these are legal moves.