added some fixes and started DeleteStore implementation

src/OperationStores/Memory.js

@@ -8,6 +8,27 @@ function copyObject (o) {
   return c
 }
 
+class DeletionStore { // eslint-disable-line
+  constructor  () {
+    this.ds = {}
+  }
+  deleteId (id) {
+    var dv = this.db[id[0]]
+    if (dv === void 0) {
+      dv = []
+      this.db[id[0]] = dv
+    }
+    for (var i in dv) {
+      if (dv[i].pos <= id[1] && id[1] < dv[i].pos + length) {
+        // within the bound, already deleted
+        return
+      } else {
+
+      }
+    }
+  }
+}
+
 Y.Memory = (function () { // eslint-disable-line no-unused-vars
   class Transaction extends AbstractTransaction { // eslint-disable-line
 

src/OperationStores/RedBlackTree.js

@@ -80,6 +80,22 @@ class N {
       return p.parent
     }
   }
+  prev () {
+    if (this.left !== null) {
+      // search the most right node in the left tree
+      var o = this.left
+      while (o.right !== null) {
+        o = o.right
+      }
+      return o
+    } else {
+      var p = this
+      while (p.parent !== null && p !== p.parent.right) {
+        p = p.parent
+      }
+      return p.parent
+    }
+  }
   rotateRight (tree) {
     var parent = this.parent
     var newParent = this.left
@@ -118,7 +134,7 @@ class RBTree { // eslint-disable-line no-unused-vars
     }
     var o = this.root
     if (o === null) {
-      return false
+      return null
     } else {
       while (true) {
         if ((from === null || smaller(from, o.val.id)) && o.left !== null) {
@@ -140,6 +156,34 @@ class RBTree { // eslint-disable-line no-unused-vars
       }
     }
   }
+  findNodeWithUpperBound (to) {
+    if (to === void 0) {
+      throw new Error('You must define from!')
+    }
+    var o = this.root
+    if (o === null) {
+      return null
+    } else {
+      while (true) {
+        if ((to === null || smaller(o.val.id, to)) && o.right !== null) {
+          // o is included in the bound
+          // try to find an element that is closer to the bound
+          o = o.right
+        } else if (to !== null && smaller(to, o.val.id)) {
+          // o is not within the bound, maybe one of the left elements is..
+          if (o.left !== null) {
+            o = o.left
+          } else {
+            // there is no left element. Search for the prev smaller element,
+            // this should be within the bounds
+            return o.prev()
+          }
+        } else {
+          return o
+        }
+      }
+    }
+  }
   iterate (from, to, f) {
     var o = this.findNodeWithLowerBound(from)
     while (o !== null && (to === null || smaller(o.val.id, to) || compareIds(o.val.id, to))) {