Pope Gregory IX
| Author(s) | Title | Reference | |
|---|---|---|---|
| F.M. Powicke | Mediaeval and Renaissance Studies. vol. II, by Richard Hunt, Raymond Klibansky | 21/, p. 40 | |
| Clement C.J. Webb | Introduction of Aristotelian learning to Oxford. Volume XXIX, by D. A. Callus | 13/, p. 84 |