+
+ # Remove the item at `k1`, `k2` and `k3`
+ fun remove_at(k1: K1, k2: K2, k3: K3)
+ do
+ var level1 = self.level1
+ var level2 = level1.get_or_null(k1)
+ if level2 == null then return
+ level2.remove_at(k2, k3)
+ end
+
+ # Remove all items
+ fun clear do level1.clear