 According to Yair Shiffman, a lost work by al-Farabi on physics, his Long Commentary on Aristotle’s Physics, was also implicitly quoted by Falaquera in his Guide to the Guide (Moreh ha-Moreh), a philosophical commentary on Maimonides’ Guide written in 1280 (Shem Tov Ibn Falaquera 2001, 234); as a matter of fact, a passage of it about the formal and material differences between the heavens and the stars is explicitly quoted and commented on by Maimonides himself in chapter 19 of part two of the Guide of the Perplexed (see Moses Maimonides 1962, 2:239).