What is unreal?

The term tuccha means in Classical Sanksrit “worthless”, “insignificant”. In Vedānta, however, it gets a more specific technical meaning, to denote the absolute unreality of chimeral entities, such as the khapuṣpa (flower in the air), which will not and cannot ever exist.

Is there really a single author of the Yogasūtra and Yogabhāṣya?

The idea that the Yogasūtra (henceforth YS) and the Yogabhāṣya (henceforth YBh) are not two distinct texts has been discussed for the first way in a systematic way by Johannes Bronkhorst in 1985 (“Patañjali and the Yoga Sūtras”, Studien zur Indologie und Iranistik). Philipp Maas in his published PhD thesis (Maas 2006) examined it again and Philipp Maas in his contribution to Eli Franco’s Periodization and Historiography of Indian Philosophy (2013) dealt with it again in greater detail.