ExtractAll​(``0)

The best member of every class under seed, from the leaves up: a
round recomputes each class from its children's current best, and the rounds stop
when one changes nothing. No recursion, so no depth to guard and no stack to exhaust;
a member that reaches back into its own class through a union is built from that
class's current best and offered like any other, and loses to it under any selection
that does not prefer the larger of two writings of one thing. Rounds are bounded by
the longest chain of classes, and capped at the class count for a selection that is
not monotone in its children.