 However, individual scholarly opinions associate Cosmas' life with the first half of the 11th century and even the early 13th century.While Cosmas never mentions the date of writing of his treatise, he does leave some chronological details.Cosmas calls the Bogomil heresy "newly-appeared" and refers to the apparently popular "John, the "new" presbyter and exarch", whom most scholars identify with early-10th-century Bulgarian writer John Exarch.