Nas and las are used for the ablative, and for isolation and inclusion.
For the actual ablative, either form may be used.
For isolation from similar things, nas is used, and from dissimilar, las.
For inclusion, nas alone may be used.
Chapter 5: Purifying obscurations through despair

Sekhar Guthok, "nine-storey son's house," the tower Marpa ordered
Milarepa to build. Photo from the Shalu Association.
In Chapter 5, Milarepa tries desperately to satisfy the demands of his teacher, Marpa. In this Unit, you will read the fifth chapter of this abridged life story while continuing to learn new grammatical constructions and expressions. You will memorize a traditional grammar verse about the particles ནས་ and ལས་, and practice word sequencing for some short Tibetan sentences. You will also learn how to spell out loud in Tibetan.
When you’re ready to study Chapter Five, begin with 5.1 Grammar Preview and 5.2 Sentence Building. With those, you should be ready to try 5.3 Reading & Translation. You should also memorize the Tibetan grammar verse, review your grammar with 5.5 Sequencing Practice, and practice your pronunciation by following along with 5.6 Reading Aloud. Finally, in 5.7 you will learn how to spell out loud in Tibetan.
Reading & Translation from the Life of Milarepa
On ནས་ and ལས་
Rearrange the following words so that they make the phrase below in correct Tibetan word order. For help, press the Colors button to color words according to their grammatical categories, or the Hint button to show word glosses when hovering over a word.
When you are finished with an example, press Mark. If your answer is correct, then press Next to move on to the next example. If your answer is incorrect, then you may have to repeat the exercise one or more times. Press the Repeat button to do so. Note that this is just to give you more practice; repeat attempts will neither help nor hurt your score. When you have attempted an exercise as many times as allowed, then press Answer to see the answer.