diff --git a/vendor/go.etcd.io/etcd/pkg/adt/interval_tree.go b/vendor/go.etcd.io/etcd/pkg/adt/interval_tree.go
new file mode 100644
index 0000000..2e5b2dd
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/pkg/adt/interval_tree.go
@@ -0,0 +1,951 @@
+// Copyright 2016 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package adt
+
+import (
+	"bytes"
+	"fmt"
+	"math"
+	"strings"
+)
+
+// Comparable is an interface for trichotomic comparisons.
+type Comparable interface {
+	// Compare gives the result of a 3-way comparison
+	// a.Compare(b) = 1 => a > b
+	// a.Compare(b) = 0 => a == b
+	// a.Compare(b) = -1 => a < b
+	Compare(c Comparable) int
+}
+
+type rbcolor int
+
+const (
+	black rbcolor = iota
+	red
+)
+
+func (c rbcolor) String() string {
+	switch c {
+	case black:
+		return "black"
+	case red:
+		return "black"
+	default:
+		panic(fmt.Errorf("unknown color %d", c))
+	}
+}
+
+// Interval implements a Comparable interval [begin, end)
+// TODO: support different sorts of intervals: (a,b), [a,b], (a, b]
+type Interval struct {
+	Begin Comparable
+	End   Comparable
+}
+
+// Compare on an interval gives == if the interval overlaps.
+func (ivl *Interval) Compare(c Comparable) int {
+	ivl2 := c.(*Interval)
+	ivbCmpBegin := ivl.Begin.Compare(ivl2.Begin)
+	ivbCmpEnd := ivl.Begin.Compare(ivl2.End)
+	iveCmpBegin := ivl.End.Compare(ivl2.Begin)
+
+	// ivl is left of ivl2
+	if ivbCmpBegin < 0 && iveCmpBegin <= 0 {
+		return -1
+	}
+
+	// iv is right of iv2
+	if ivbCmpEnd >= 0 {
+		return 1
+	}
+
+	return 0
+}
+
+type intervalNode struct {
+	// iv is the interval-value pair entry.
+	iv IntervalValue
+	// max endpoint of all descendent nodes.
+	max Comparable
+	// left and right are sorted by low endpoint of key interval
+	left, right *intervalNode
+	// parent is the direct ancestor of the node
+	parent *intervalNode
+	c      rbcolor
+}
+
+func (x *intervalNode) color(sentinel *intervalNode) rbcolor {
+	if x == sentinel {
+		return black
+	}
+	return x.c
+}
+
+func (x *intervalNode) height(sentinel *intervalNode) int {
+	if x == sentinel {
+		return 0
+	}
+	ld := x.left.height(sentinel)
+	rd := x.right.height(sentinel)
+	if ld < rd {
+		return rd + 1
+	}
+	return ld + 1
+}
+
+func (x *intervalNode) min(sentinel *intervalNode) *intervalNode {
+	for x.left != sentinel {
+		x = x.left
+	}
+	return x
+}
+
+// successor is the next in-order node in the tree
+func (x *intervalNode) successor(sentinel *intervalNode) *intervalNode {
+	if x.right != sentinel {
+		return x.right.min(sentinel)
+	}
+	y := x.parent
+	for y != sentinel && x == y.right {
+		x = y
+		y = y.parent
+	}
+	return y
+}
+
+// updateMax updates the maximum values for a node and its ancestors
+func (x *intervalNode) updateMax(sentinel *intervalNode) {
+	for x != sentinel {
+		oldmax := x.max
+		max := x.iv.Ivl.End
+		if x.left != sentinel && x.left.max.Compare(max) > 0 {
+			max = x.left.max
+		}
+		if x.right != sentinel && x.right.max.Compare(max) > 0 {
+			max = x.right.max
+		}
+		if oldmax.Compare(max) == 0 {
+			break
+		}
+		x.max = max
+		x = x.parent
+	}
+}
+
+type nodeVisitor func(n *intervalNode) bool
+
+// visit will call a node visitor on each node that overlaps the given interval
+func (x *intervalNode) visit(iv *Interval, sentinel *intervalNode, nv nodeVisitor) bool {
+	if x == sentinel {
+		return true
+	}
+	v := iv.Compare(&x.iv.Ivl)
+	switch {
+	case v < 0:
+		if !x.left.visit(iv, sentinel, nv) {
+			return false
+		}
+	case v > 0:
+		maxiv := Interval{x.iv.Ivl.Begin, x.max}
+		if maxiv.Compare(iv) == 0 {
+			if !x.left.visit(iv, sentinel, nv) || !x.right.visit(iv, sentinel, nv) {
+				return false
+			}
+		}
+	default:
+		if !x.left.visit(iv, sentinel, nv) || !nv(x) || !x.right.visit(iv, sentinel, nv) {
+			return false
+		}
+	}
+	return true
+}
+
+// IntervalValue represents a range tree node that contains a range and a value.
+type IntervalValue struct {
+	Ivl Interval
+	Val interface{}
+}
+
+// IntervalTree represents a (mostly) textbook implementation of the
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.) chapter 13 red-black tree
+// and chapter 14.3 interval tree with search supporting "stabbing queries".
+type IntervalTree interface {
+	// Insert adds a node with the given interval into the tree.
+	Insert(ivl Interval, val interface{})
+	// Delete removes the node with the given interval from the tree, returning
+	// true if a node is in fact removed.
+	Delete(ivl Interval) bool
+	// Len gives the number of elements in the tree.
+	Len() int
+	// Height is the number of levels in the tree; one node has height 1.
+	Height() int
+	// MaxHeight is the expected maximum tree height given the number of nodes.
+	MaxHeight() int
+	// Visit calls a visitor function on every tree node intersecting the given interval.
+	// It will visit each interval [x, y) in ascending order sorted on x.
+	Visit(ivl Interval, ivv IntervalVisitor)
+	// Find gets the IntervalValue for the node matching the given interval
+	Find(ivl Interval) *IntervalValue
+	// Intersects returns true if there is some tree node intersecting the given interval.
+	Intersects(iv Interval) bool
+	// Contains returns true if the interval tree's keys cover the entire given interval.
+	Contains(ivl Interval) bool
+	// Stab returns a slice with all elements in the tree intersecting the interval.
+	Stab(iv Interval) []*IntervalValue
+	// Union merges a given interval tree into the receiver.
+	Union(inIvt IntervalTree, ivl Interval)
+}
+
+// NewIntervalTree returns a new interval tree.
+func NewIntervalTree() IntervalTree {
+	sentinel := &intervalNode{
+		iv:     IntervalValue{},
+		max:    nil,
+		left:   nil,
+		right:  nil,
+		parent: nil,
+		c:      black,
+	}
+	return &intervalTree{
+		root:     sentinel,
+		count:    0,
+		sentinel: sentinel,
+	}
+}
+
+type intervalTree struct {
+	root  *intervalNode
+	count int
+
+	// red-black NIL node
+	// use 'sentinel' as a dummy object to simplify boundary conditions
+	// use the sentinel to treat a nil child of a node x as an ordinary node whose parent is x
+	// use one shared sentinel to represent all nil leaves and the root's parent
+	sentinel *intervalNode
+}
+
+// TODO: make this consistent with textbook implementation
+//
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.4, p324
+//
+//	 0. RB-DELETE(T, z)
+//	 1.
+//	 2. y = z
+//	 3. y-original-color = y.color
+//	 4.
+//	 5. if z.left == T.nil
+//	 6. 	x = z.right
+//	 7. 	RB-TRANSPLANT(T, z, z.right)
+//	 8. else if z.right == T.nil
+//	 9. 	x = z.left
+//	10. 	RB-TRANSPLANT(T, z, z.left)
+//	11. else
+//	12. 	y = TREE-MINIMUM(z.right)
+//	13. 	y-original-color = y.color
+//	14. 	x = y.right
+//	15. 	if y.p == z
+//	16. 		x.p = y
+//	17. 	else
+//	18. 		RB-TRANSPLANT(T, y, y.right)
+//	19. 		y.right = z.right
+//	20. 		y.right.p = y
+//	21. 	RB-TRANSPLANT(T, z, y)
+//	22. 	y.left = z.left
+//	23. 	y.left.p = y
+//	24. 	y.color = z.color
+//	25.
+//	26. if y-original-color == BLACK
+//	27. 	RB-DELETE-FIXUP(T, x)
+
+// Delete removes the node with the given interval from the tree, returning
+// true if a node is in fact removed.
+func (ivt *intervalTree) Delete(ivl Interval) bool {
+	z := ivt.find(ivl)
+	if z == ivt.sentinel {
+		return false
+	}
+
+	y := z
+	if z.left != ivt.sentinel && z.right != ivt.sentinel {
+		y = z.successor(ivt.sentinel)
+	}
+
+	x := ivt.sentinel
+	if y.left != ivt.sentinel {
+		x = y.left
+	} else if y.right != ivt.sentinel {
+		x = y.right
+	}
+
+	x.parent = y.parent
+
+	if y.parent == ivt.sentinel {
+		ivt.root = x
+	} else {
+		if y == y.parent.left {
+			y.parent.left = x
+		} else {
+			y.parent.right = x
+		}
+		y.parent.updateMax(ivt.sentinel)
+	}
+	if y != z {
+		z.iv = y.iv
+		z.updateMax(ivt.sentinel)
+	}
+
+	if y.color(ivt.sentinel) == black {
+		ivt.deleteFixup(x)
+	}
+
+	ivt.count--
+	return true
+}
+
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.4, p326
+//
+//	 0. RB-DELETE-FIXUP(T, z)
+//	 1.
+//	 2. while x ≠ T.root and x.color == BLACK
+//	 3. 	if x == x.p.left
+//	 4. 		w = x.p.right
+//	 5. 		if w.color == RED
+//	 6. 			w.color = BLACK
+//	 7. 			x.p.color = RED
+//	 8. 			LEFT-ROTATE(T, x, p)
+//	 9. 		if w.left.color == BLACK and w.right.color == BLACK
+//	10. 			w.color = RED
+//	11. 			x = x.p
+//	12. 		else if w.right.color == BLACK
+//	13. 				w.left.color = BLACK
+//	14. 				w.color = RED
+//	15. 				RIGHT-ROTATE(T, w)
+//	16. 				w = w.p.right
+//	17. 			w.color = x.p.color
+//	18. 			x.p.color = BLACK
+//	19. 			LEFT-ROTATE(T, w.p)
+//	20. 			x = T.root
+//	21. 	else
+//	22. 		w = x.p.left
+//	23. 		if w.color == RED
+//	24. 			w.color = BLACK
+//	25. 			x.p.color = RED
+//	26. 			RIGHT-ROTATE(T, x, p)
+//	27. 		if w.right.color == BLACK and w.left.color == BLACK
+//	28. 			w.color = RED
+//	29. 			x = x.p
+//	30. 		else if w.left.color == BLACK
+//	31. 				w.right.color = BLACK
+//	32. 				w.color = RED
+//	33. 				LEFT-ROTATE(T, w)
+//	34. 				w = w.p.left
+//	35. 			w.color = x.p.color
+//	36. 			x.p.color = BLACK
+//	37. 			RIGHT-ROTATE(T, w.p)
+//	38. 			x = T.root
+//	39.
+//	40. x.color = BLACK
+//
+func (ivt *intervalTree) deleteFixup(x *intervalNode) {
+	for x != ivt.root && x.color(ivt.sentinel) == black {
+		if x == x.parent.left { // line 3-20
+			w := x.parent.right
+			if w.color(ivt.sentinel) == red {
+				w.c = black
+				x.parent.c = red
+				ivt.rotateLeft(x.parent)
+				w = x.parent.right
+			}
+			if w == nil {
+				break
+			}
+			if w.left.color(ivt.sentinel) == black && w.right.color(ivt.sentinel) == black {
+				w.c = red
+				x = x.parent
+			} else {
+				if w.right.color(ivt.sentinel) == black {
+					w.left.c = black
+					w.c = red
+					ivt.rotateRight(w)
+					w = x.parent.right
+				}
+				w.c = x.parent.color(ivt.sentinel)
+				x.parent.c = black
+				w.right.c = black
+				ivt.rotateLeft(x.parent)
+				x = ivt.root
+			}
+		} else { // line 22-38
+			// same as above but with left and right exchanged
+			w := x.parent.left
+			if w.color(ivt.sentinel) == red {
+				w.c = black
+				x.parent.c = red
+				ivt.rotateRight(x.parent)
+				w = x.parent.left
+			}
+			if w == nil {
+				break
+			}
+			if w.left.color(ivt.sentinel) == black && w.right.color(ivt.sentinel) == black {
+				w.c = red
+				x = x.parent
+			} else {
+				if w.left.color(ivt.sentinel) == black {
+					w.right.c = black
+					w.c = red
+					ivt.rotateLeft(w)
+					w = x.parent.left
+				}
+				w.c = x.parent.color(ivt.sentinel)
+				x.parent.c = black
+				w.left.c = black
+				ivt.rotateRight(x.parent)
+				x = ivt.root
+			}
+		}
+	}
+
+	if x != nil {
+		x.c = black
+	}
+}
+
+func (ivt *intervalTree) createIntervalNode(ivl Interval, val interface{}) *intervalNode {
+	return &intervalNode{
+		iv:     IntervalValue{ivl, val},
+		max:    ivl.End,
+		c:      red,
+		left:   ivt.sentinel,
+		right:  ivt.sentinel,
+		parent: ivt.sentinel,
+	}
+}
+
+// TODO: make this consistent with textbook implementation
+//
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.3, p315
+//
+//	 0. RB-INSERT(T, z)
+//	 1.
+//	 2. y = T.nil
+//	 3. x = T.root
+//	 4.
+//	 5. while x ≠ T.nil
+//	 6. 	y = x
+//	 7. 	if z.key < x.key
+//	 8. 		x = x.left
+//	 9. 	else
+//	10. 		x = x.right
+//	11.
+//	12. z.p = y
+//	13.
+//	14. if y == T.nil
+//	15. 	T.root = z
+//	16. else if z.key < y.key
+//	17. 	y.left = z
+//	18. else
+//	19. 	y.right = z
+//	20.
+//	21. z.left = T.nil
+//	22. z.right = T.nil
+//	23. z.color = RED
+//	24.
+//	25. RB-INSERT-FIXUP(T, z)
+
+// Insert adds a node with the given interval into the tree.
+func (ivt *intervalTree) Insert(ivl Interval, val interface{}) {
+	y := ivt.sentinel
+	z := ivt.createIntervalNode(ivl, val)
+	x := ivt.root
+	for x != ivt.sentinel {
+		y = x
+		if z.iv.Ivl.Begin.Compare(x.iv.Ivl.Begin) < 0 {
+			x = x.left
+		} else {
+			x = x.right
+		}
+	}
+
+	z.parent = y
+	if y == ivt.sentinel {
+		ivt.root = z
+	} else {
+		if z.iv.Ivl.Begin.Compare(y.iv.Ivl.Begin) < 0 {
+			y.left = z
+		} else {
+			y.right = z
+		}
+		y.updateMax(ivt.sentinel)
+	}
+	z.c = red
+
+	ivt.insertFixup(z)
+	ivt.count++
+}
+
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.3, p316
+//
+//	 0. RB-INSERT-FIXUP(T, z)
+//	 1.
+//	 2. while z.p.color == RED
+//	 3. 	if z.p == z.p.p.left
+//	 4. 		y = z.p.p.right
+//	 5. 		if y.color == RED
+//	 6. 			z.p.color = BLACK
+//	 7. 			y.color = BLACK
+//	 8. 			z.p.p.color = RED
+//	 9. 			z = z.p.p
+//	10. 		else if z == z.p.right
+//	11. 				z = z.p
+//	12. 				LEFT-ROTATE(T, z)
+//	13. 			z.p.color = BLACK
+//	14. 			z.p.p.color = RED
+//	15. 			RIGHT-ROTATE(T, z.p.p)
+//	16. 	else
+//	17. 		y = z.p.p.left
+//	18. 		if y.color == RED
+//	19. 			z.p.color = BLACK
+//	20. 			y.color = BLACK
+//	21. 			z.p.p.color = RED
+//	22. 			z = z.p.p
+//	23. 		else if z == z.p.right
+//	24. 				z = z.p
+//	25. 				RIGHT-ROTATE(T, z)
+//	26. 			z.p.color = BLACK
+//	27. 			z.p.p.color = RED
+//	28. 			LEFT-ROTATE(T, z.p.p)
+//	29.
+//	30. T.root.color = BLACK
+//
+func (ivt *intervalTree) insertFixup(z *intervalNode) {
+	for z.parent.color(ivt.sentinel) == red {
+		if z.parent == z.parent.parent.left { // line 3-15
+
+			y := z.parent.parent.right
+			if y.color(ivt.sentinel) == red {
+				y.c = black
+				z.parent.c = black
+				z.parent.parent.c = red
+				z = z.parent.parent
+			} else {
+				if z == z.parent.right {
+					z = z.parent
+					ivt.rotateLeft(z)
+				}
+				z.parent.c = black
+				z.parent.parent.c = red
+				ivt.rotateRight(z.parent.parent)
+			}
+		} else { // line 16-28
+			// same as then with left/right exchanged
+			y := z.parent.parent.left
+			if y.color(ivt.sentinel) == red {
+				y.c = black
+				z.parent.c = black
+				z.parent.parent.c = red
+				z = z.parent.parent
+			} else {
+				if z == z.parent.left {
+					z = z.parent
+					ivt.rotateRight(z)
+				}
+				z.parent.c = black
+				z.parent.parent.c = red
+				ivt.rotateLeft(z.parent.parent)
+			}
+		}
+	}
+
+	// line 30
+	ivt.root.c = black
+}
+
+// rotateLeft moves x so it is left of its right child
+//
+// "Introduction to Algorithms" (Cormen et al, 3rd ed.), chapter 13.2, p313
+//
+//	 0. LEFT-ROTATE(T, x)
+//	 1.
+//	 2. y = x.right
+//	 3. x.right = y.left
+//	 4.
+//	 5. if y.left ≠ T.nil
+//	 6. 	y.left.p = x
+//	 7.
+//	 8. y.p = x.p
+//	 9.
+//	10. if x.p == T.nil
+//	11. 	T.root = y
+//	12. else if x == x.p.left
+//	13. 	x.p.left = y
+//	14. else
+//	15. 	x.p.right = y
+//	16.
+//	17. y.left = x
+//	18. x.p = y
+//
+func (ivt *intervalTree) rotateLeft(x *intervalNode) {
+	// rotateLeft x must have right child
+	if x.right == ivt.sentinel {
+		return
+	}
+
+	// line 2-3
+	y := x.right
+	x.right = y.left
+
+	// line 5-6
+	if y.left != ivt.sentinel {
+		y.left.parent = x
+	}
+	x.updateMax(ivt.sentinel)
+
+	// line 10-15, 18
+	ivt.replaceParent(x, y)
+
+	// line 17
+	y.left = x
+	y.updateMax(ivt.sentinel)
+}
+
+// rotateRight moves x so it is right of its left child
+//
+//	 0. RIGHT-ROTATE(T, x)
+//	 1.
+//	 2. y = x.left
+//	 3. x.left = y.right
+//	 4.
+//	 5. if y.right ≠ T.nil
+//	 6. 	y.right.p = x
+//	 7.
+//	 8. y.p = x.p
+//	 9.
+//	10. if x.p == T.nil
+//	11. 	T.root = y
+//	12. else if x == x.p.right
+//	13. 	x.p.right = y
+//	14. else
+//	15. 	x.p.left = y
+//	16.
+//	17. y.right = x
+//	18. x.p = y
+//
+func (ivt *intervalTree) rotateRight(x *intervalNode) {
+	// rotateRight x must have left child
+	if x.left == ivt.sentinel {
+		return
+	}
+
+	// line 2-3
+	y := x.left
+	x.left = y.right
+
+	// line 5-6
+	if y.right != ivt.sentinel {
+		y.right.parent = x
+	}
+	x.updateMax(ivt.sentinel)
+
+	// line 10-15, 18
+	ivt.replaceParent(x, y)
+
+	// line 17
+	y.right = x
+	y.updateMax(ivt.sentinel)
+}
+
+// replaceParent replaces x's parent with y
+func (ivt *intervalTree) replaceParent(x *intervalNode, y *intervalNode) {
+	y.parent = x.parent
+	if x.parent == ivt.sentinel {
+		ivt.root = y
+	} else {
+		if x == x.parent.left {
+			x.parent.left = y
+		} else {
+			x.parent.right = y
+		}
+		x.parent.updateMax(ivt.sentinel)
+	}
+	x.parent = y
+}
+
+// Len gives the number of elements in the tree
+func (ivt *intervalTree) Len() int { return ivt.count }
+
+// Height is the number of levels in the tree; one node has height 1.
+func (ivt *intervalTree) Height() int { return ivt.root.height(ivt.sentinel) }
+
+// MaxHeight is the expected maximum tree height given the number of nodes
+func (ivt *intervalTree) MaxHeight() int {
+	return int((2 * math.Log2(float64(ivt.Len()+1))) + 0.5)
+}
+
+// IntervalVisitor is used on tree searches; return false to stop searching.
+type IntervalVisitor func(n *IntervalValue) bool
+
+// Visit calls a visitor function on every tree node intersecting the given interval.
+// It will visit each interval [x, y) in ascending order sorted on x.
+func (ivt *intervalTree) Visit(ivl Interval, ivv IntervalVisitor) {
+	ivt.root.visit(&ivl, ivt.sentinel, func(n *intervalNode) bool { return ivv(&n.iv) })
+}
+
+// find the exact node for a given interval
+func (ivt *intervalTree) find(ivl Interval) *intervalNode {
+	ret := ivt.sentinel
+	f := func(n *intervalNode) bool {
+		if n.iv.Ivl != ivl {
+			return true
+		}
+		ret = n
+		return false
+	}
+	ivt.root.visit(&ivl, ivt.sentinel, f)
+	return ret
+}
+
+// Find gets the IntervalValue for the node matching the given interval
+func (ivt *intervalTree) Find(ivl Interval) (ret *IntervalValue) {
+	n := ivt.find(ivl)
+	if n == ivt.sentinel {
+		return nil
+	}
+	return &n.iv
+}
+
+// Intersects returns true if there is some tree node intersecting the given interval.
+func (ivt *intervalTree) Intersects(iv Interval) bool {
+	x := ivt.root
+	for x != ivt.sentinel && iv.Compare(&x.iv.Ivl) != 0 {
+		if x.left != ivt.sentinel && x.left.max.Compare(iv.Begin) > 0 {
+			x = x.left
+		} else {
+			x = x.right
+		}
+	}
+	return x != ivt.sentinel
+}
+
+// Contains returns true if the interval tree's keys cover the entire given interval.
+func (ivt *intervalTree) Contains(ivl Interval) bool {
+	var maxEnd, minBegin Comparable
+
+	isContiguous := true
+	ivt.Visit(ivl, func(n *IntervalValue) bool {
+		if minBegin == nil {
+			minBegin = n.Ivl.Begin
+			maxEnd = n.Ivl.End
+			return true
+		}
+		if maxEnd.Compare(n.Ivl.Begin) < 0 {
+			isContiguous = false
+			return false
+		}
+		if n.Ivl.End.Compare(maxEnd) > 0 {
+			maxEnd = n.Ivl.End
+		}
+		return true
+	})
+
+	return isContiguous && minBegin != nil && maxEnd.Compare(ivl.End) >= 0 && minBegin.Compare(ivl.Begin) <= 0
+}
+
+// Stab returns a slice with all elements in the tree intersecting the interval.
+func (ivt *intervalTree) Stab(iv Interval) (ivs []*IntervalValue) {
+	if ivt.count == 0 {
+		return nil
+	}
+	f := func(n *IntervalValue) bool { ivs = append(ivs, n); return true }
+	ivt.Visit(iv, f)
+	return ivs
+}
+
+// Union merges a given interval tree into the receiver.
+func (ivt *intervalTree) Union(inIvt IntervalTree, ivl Interval) {
+	f := func(n *IntervalValue) bool {
+		ivt.Insert(n.Ivl, n.Val)
+		return true
+	}
+	inIvt.Visit(ivl, f)
+}
+
+type visitedInterval struct {
+	root  Interval
+	left  Interval
+	right Interval
+	color rbcolor
+	depth int
+}
+
+func (vi visitedInterval) String() string {
+	bd := new(strings.Builder)
+	bd.WriteString(fmt.Sprintf("root [%v,%v,%v], left [%v,%v], right [%v,%v], depth %d",
+		vi.root.Begin, vi.root.End, vi.color,
+		vi.left.Begin, vi.left.End,
+		vi.right.Begin, vi.right.End,
+		vi.depth,
+	))
+	return bd.String()
+}
+
+// visitLevel traverses tree in level order.
+// used for testing
+func (ivt *intervalTree) visitLevel() []visitedInterval {
+	if ivt.root == ivt.sentinel {
+		return nil
+	}
+
+	rs := make([]visitedInterval, 0, ivt.Len())
+
+	type pair struct {
+		node  *intervalNode
+		depth int
+	}
+	queue := []pair{{ivt.root, 0}}
+	for len(queue) > 0 {
+		f := queue[0]
+		queue = queue[1:]
+
+		vi := visitedInterval{
+			root:  f.node.iv.Ivl,
+			color: f.node.color(ivt.sentinel),
+			depth: f.depth,
+		}
+		if f.node.left != ivt.sentinel {
+			vi.left = f.node.left.iv.Ivl
+			queue = append(queue, pair{f.node.left, f.depth + 1})
+		}
+		if f.node.right != ivt.sentinel {
+			vi.right = f.node.right.iv.Ivl
+			queue = append(queue, pair{f.node.right, f.depth + 1})
+		}
+
+		rs = append(rs, vi)
+	}
+
+	return rs
+}
+
+type StringComparable string
+
+func (s StringComparable) Compare(c Comparable) int {
+	sc := c.(StringComparable)
+	if s < sc {
+		return -1
+	}
+	if s > sc {
+		return 1
+	}
+	return 0
+}
+
+func NewStringInterval(begin, end string) Interval {
+	return Interval{StringComparable(begin), StringComparable(end)}
+}
+
+func NewStringPoint(s string) Interval {
+	return Interval{StringComparable(s), StringComparable(s + "\x00")}
+}
+
+// StringAffineComparable treats "" as > all other strings
+type StringAffineComparable string
+
+func (s StringAffineComparable) Compare(c Comparable) int {
+	sc := c.(StringAffineComparable)
+
+	if len(s) == 0 {
+		if len(sc) == 0 {
+			return 0
+		}
+		return 1
+	}
+	if len(sc) == 0 {
+		return -1
+	}
+
+	if s < sc {
+		return -1
+	}
+	if s > sc {
+		return 1
+	}
+	return 0
+}
+
+func NewStringAffineInterval(begin, end string) Interval {
+	return Interval{StringAffineComparable(begin), StringAffineComparable(end)}
+}
+
+func NewStringAffinePoint(s string) Interval {
+	return NewStringAffineInterval(s, s+"\x00")
+}
+
+func NewInt64Interval(a int64, b int64) Interval {
+	return Interval{Int64Comparable(a), Int64Comparable(b)}
+}
+
+func newInt64EmptyInterval() Interval {
+	return Interval{Begin: nil, End: nil}
+}
+
+func NewInt64Point(a int64) Interval {
+	return Interval{Int64Comparable(a), Int64Comparable(a + 1)}
+}
+
+type Int64Comparable int64
+
+func (v Int64Comparable) Compare(c Comparable) int {
+	vc := c.(Int64Comparable)
+	cmp := v - vc
+	if cmp < 0 {
+		return -1
+	}
+	if cmp > 0 {
+		return 1
+	}
+	return 0
+}
+
+// BytesAffineComparable treats empty byte arrays as > all other byte arrays
+type BytesAffineComparable []byte
+
+func (b BytesAffineComparable) Compare(c Comparable) int {
+	bc := c.(BytesAffineComparable)
+
+	if len(b) == 0 {
+		if len(bc) == 0 {
+			return 0
+		}
+		return 1
+	}
+	if len(bc) == 0 {
+		return -1
+	}
+
+	return bytes.Compare(b, bc)
+}
+
+func NewBytesAffineInterval(begin, end []byte) Interval {
+	return Interval{BytesAffineComparable(begin), BytesAffineComparable(end)}
+}
+
+func NewBytesAffinePoint(b []byte) Interval {
+	be := make([]byte, len(b)+1)
+	copy(be, b)
+	be[len(b)] = 0
+	return NewBytesAffineInterval(b, be)
+}