found: His Qui in comincia illibro chiamato Thesoro de poueri, ca. 1497: t.p. (Piero Spano)
found: LC manual cat. (hdg.: Joannes XXI, Pope, d. 1277; usage: Pedro Hispano, Peter of Spain, Pietro Spano)
found: Encyc. Brit., 15th ed., c1983 (John XXI; orig. name, Petrus Juliani, also called Peter of Spain; b. c. 1210-20, Lisbon; d. 5/20/1277, Viterbo, Italy; pope, 1276-77; wrote one of the most widely-used medieval textbooks on logic, Summulae logicales)
found: Encyc. of philosophy, c1967 (Peter of Spain, or Petrus Hispanus, Petrus Juliani (1210/1220-1277); logician, philosopher, pope; author of Summulae logicales)
found: His Tractatus, called afterwards, Summule logicales, 1972, 1973: t.p. (Peter of Spain (Petrus Hispanus Portugalensis)) p. ix, etc. (identification with Pope John XXI disputed; may have been Petrus Alfonsi, O.P., or Petrus Ferrandi Hispanus (d. 1254-1259?))
found: New Cath. encyc., c1967 (John XXI, Pope (Peter of Spain); b. Petrus Juliani or Petrus Hispanus, Lisbon, between c. 1210 and 1215; his best-known work, the Summulae logicales)
found: BL database, 1 Nov. 2002 (ref.: Rebello, Pedro Juli ao)
found: John XXI, Pope. Il tesoro dei poveri, c2007: t.p. (Pietro Ispano (Papa Giovanni XXI))
John XXI, Pope, -1277
