code: func (ot *orderedTree) Apply(interval Interval, fn func(Entry) bool) {
  	ot.apply(ot.top, interval, 1, func(n *node) bool {
  		return fn(n.entry)
  	})
  }
docs: // Apply will call (in order) the provided function to every
  // entry that falls within the provided interval.  Any alteration
  // the the entry that would result in different answers to the
  // interface methods results in undefined behavior.