open(x, y, iter) = erosions(x, y, iter) : dilations(x, y, iter);
close(x, y, iter) = dilations(x, y, iter) : erosions(x, y, iter);
open(x, y, iter) = erosions(x, y, iter) : dilations(x, y, iter);
close(x, y, iter) = dilations(x, y, iter) : erosions(x, y, iter);