 Independent treatises on individual subjects written by Avicenna deal with most subjects, but especially with those for which there was greater demand by his sponsors and in which he was particularly interested, notably logic, the soul, and the metaphysics of the rational soul. In an effort to reach a wider audience, he expressed his theories on the rational soul in two allegories, Alive, Son of Awake (Ḥayy b. Yaqẓān, GM 7; Goichon 1959) and The Bird (GM 8; Heath 1990), and he versified still others: The Divine Pearl (al-Jumāna al-ilāhiyya) on the oneness of God and the emanated creation in 334 verses (GM 9), The Science of Logic, in verse, in 290 lines (GL 4), and a number of poems on medical subjects, notably his Medicine, in verse, in 1326 lines (GMed 27), which was commented upon by Averroes. In addition, he engaged in protracted correspondence with scholars who asked or questioned him about specific problems;  noteworthy are his Answers to Questions Posed by Bīrūnī [GP 8], the other scientific genius of his time, on Aristotelian physics and cosmology, and especially the two posthumous compilations of his responses and discussions circulating under the titles Notes (GS 12a) and Discussions (GS 14). He also wrote what amounts to open letters depicting the controversies in which he was involved and seeking arbitration or repudiating calumniatory charges against him (GPW 1–3).