Extract the answer to the question from the following context. Question: What is considered a good text on this matteR? Context: A core problem in the study of early Buddhism is the relation between dhyana and insight. Schmithausen, in his often-cited article On some Aspects of Descriptions or Theories of 'Liberating Insight' and 'Enlightenment' in Early Buddhism notes that the mention of the four noble truths as constituting "liberating insight", which is attained after mastering the Rupa Jhanas, is a later addition to texts such as Majjhima Nikaya 36.[page needed]
The answer to this question is:
On some Aspects of Descriptions or Theories of 'Liberating Insight' and 'Enlightenment' in Early Buddhism