 As to the date, in the 19th century F. Dieterici proposed 961 to 986, basing his estimate on the work of the seventeenth century lexicographer Hâjjî Khalîfa and on the presence in the treatises of verses by the famous poet al-Mutanabbî (d. 965). Massignon (1913) used a verse by the poet Ibn al-Rûmî (d. 896) to establish these years as the earliest possible date (cf. also Hamdani 1999, 76; Hamdani, Soufan 2019, 12; 28–29), and took the latest possible date to be the one indicated by the definition of sine (al-jayb) given by the Ikhwân. Such definition is not yet the one provided by al-Battânî (d. 929; reference to vol. I, p. 46 of the Bombay ed., 1887-1889, corresponding to I, 86, 14–15 of the Beirut edition referred to in this article). The “expected event” frequently mentioned in the encyclopedia would then be the Fatimid conquest of Egypt, which can be traced back to those years. On the basis of astronomical data, Casanova (1915) moved the dates about a century forward, assigning the work to the years 1047–51.