Would you please give me the author to whom you refer...as well as the book title? Is this book available in English, or is it written in another language? Did you try searching for the 'relationship between Christianity and Islam co-existing on the African continent, sharing fifteen hundred years-of-history'? (or you might simply say, co-sharing fifteen hundred years-of-history on the African continent and leave co-existing out of the search parameter). Let me know if these ideas help you.