Questions & Answers about خوابیدن در کلاس آزاد نیست.
Why does خوابیدن translate to "sleeping" here instead of "to sleep"?
In Farsi, the infinitive form (which always ends in -dan or -tan) is often used as a noun, similar to English words ending in "-ing". So خوابیدن means both "to sleep" and "sleeping". Here, the action of sleeping acts as the subject of the sentence.
How do I extract the present stem from خوابیدن?
While past stems are easily found by dropping the final -n from the infinitive, present stems are often irregular and must be memorized. For خوابیدن, the present stem is خواب (khaab).
I learned that آزاد means "free". Why is it translated as "allowed" here?
You are right, آزاد literally means "free". In Farsi, describing an activity as "free" in a certain context is the natural way to say it is unrestricted, permitted, or "allowed".
Why is the sentence using نیست instead of the regular word for "no"?
نیست specifically means "is not". It is the negative version of the verb است (is). The standard word for "no" is نه, but if you used that here, your sentence would be missing a verb.