GirĂ³n Sierra, Francisco Javier (2016). Willis's "On Vaults of the Middle Ages" some notes about his heuristic approach, his drawing and Viollet-le-Duc's reception. In: "Robert Willis (1800-1875) International Symposium", 16-17 septiembre 2016, Gonville and Caius College, Cambridge UK. ISBN 978-84-946000-0-5. pp. 167-208.