The Definitive Work Regarding Shaykh 'Isa of Segovia:

The definitive work on the subject of Shaykh 'Isa of Segovia and a brilliant, masterful work of research and scholarship in its own right:

Islamic Literature in Spanish and Aljamiado:

Yça of Segovia (fl. 1450), His Antecendents and Successors

of G.A. Wiegers; read about it here:

http://books.google.com/books/about/Islamic_Literature_in_Spanish_and_Aljami.html?id=Z2A55_kw3F4C