Petrus Hispanus

The most important rules of syllogism are summed up in the following mnemonic lines, which appear to have been perfected, though not invented, by a mediæval logician known as Petrus Hispanus, who was afterwards raised to the Papal Chair under the title of Pope John XXI, and who died in 1277 --

Deductive Logic St. George William Joseph Stock

One of the most popular works, the "Thesaurus Pauperum," was written by Petrus Hispanus, afterwards Pope John XXI.

The Evolution of Modern Medicine 1921

-- Petrus Hispanus de morte et vita, et causis longitudinis et brevitatis vitæ.

The Private Diary of Dr. John Dee And the Catalog of His Library of Manuscripts John Dee 1567

Pauperum, "was written by Petrus Hispanus, afterwards Pope John XXI.

The Evolution of Modern Medicine A Series of Lectures Delivered at Yale University on the Silliman Foundation in April, 1913 William Osler 1884