MLA

John XXI, Pope, -1277. Thesaurus pauperum. beteen 1400 and 1499.. https://collections.library.yale.edu/catalog/16960333.

APA, 6th edition

John XXI, Pope, -1277. (beteen 1400 and 1499.)[Thesaurus pauperum]. https://collections.library.yale.edu/catalog/16960333.