Dear André, I am extremely saddened by the news of Eduardo passing away. I happen to be one of the hundreds of very lucky students whom Eduardo, as the maestro that he was, taught how to think about and develop mathematics categorically. This no doubt shaped my subsequent research and teaching, and for it I will always be grateful and indebted. Eduardo's research was original and pioneering, deep and far reaching, and shall remain relevant and significant. I last interacted with him in person around a year ago, and he was still thinking about research. We had a nice mathematical discussion which we hoped to continue; sadly, this will now not happen. Marcelo On Thu, 30 Jul 2026 at 03:21, Joyal, André via Categories < categories-list@categories.org.au> wrote:
Dear category theorists,
Sad news. My friend Eduardo Dubuc passed away Monday (July 27, 2026) after having a stroke. while teaching math at the University of Buenos-Aires. He was almost 84. He was visiting professor at UQAM until 1980, and professor at the UBA until his death.
Eduardo received his Phd in 1969 from the University of Chicago under the supervision of Saunders MacLane with a thesis on *Kan extension in enriched categories*. His SLN monograph on the subject was the first systematic theory of enriched colimits and of enriched Kan extensions. Eduardo worked on a large variety of subjects throughout his life.
https://scholar.google.com/citations?user=3fiEMcgAAAAJ&hl=en
To illustrate the diversity of his work I will give a few examples. He introduced the *Elevator Calculus* for 2-categories around 1970, a precursor of Penrose diagrams and of *string diagrams* developed 15 years later by Ross Street and myself for applications to monoidal categories. He introduced and developed a theory of *Tannaka duality for localic groups *in a topos, with applications to the Grothendieck Galois theory developed by Myles Tierney and myself. He developed a theory of *quasi-topoi* with Jacques Penon, later included in the *Sketches of an Elephant *by P.T. Johnstone. He constructed the first full model of *synthetic differential *geometry in collaboration with Marta Bunge and Jacques Penon, it became the backbone of the book by Gonzalo Reyes and Ieke Moerdijk. He extended *Stone duality to *MV-algebras in collaboration with Roberto Cignoli et Daniele Mundici. He introduced a notion of *Quillen model 2-category* and a theory of *2-localizations* with M.E. Descotte and Martin Szyld. He gave a construction of the 2-filtered bicolimits of bicategories in collaboration with Ross Street. His work has applications in every corner of category theory.
Eduardo was a problem solver with the skills of a theory builder. He was a pleasant person to work with, eager to explore new territories. He was also a great math teacher.
See you later Eduardo, André
_______________________________________________ Categories mailing list -- categories-list@categories.org.au To unsubscribe send an email to categories-list-leave@categories.org.au