Very sad news, Andre'! My sentiments to you and all of Eduardo's friends. --Valeria On Thu, Jul 30, 2026 at 4:29 AM 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
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