Now we use special treatment for +inf. This could be simplified by including the largest split value in the last bucket. E.g., (x1, x2, x3) defines buckets [x1, x2) and [x2, x3]. This shouldn't affect user code much, and there are applications that need to include the right-most value. For example, we can bucketize ratings from 0 to 10 to bad, neutral, and good with splits 0, 4, 6, 10.