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**Anne Sjerp Troelstra (1939-2019)**

**Anne Sjerp Troelstra** (Maartensdijk,1939– Blaricum, 2019)was full professor of pure mathematics and foundations of mathematics at the University of Amsterdam. He described his research interests as ‘history and philosophy of constructivism; metamathematics of systems based on intuitionistic logic; proof theory'. Parts of his work have been taken up in computer science as well. Troelstra was an academic grandson of L.E.J. Brouwer, and began his contributions to the latter’s foundational program with the dissertation Intuitionistic General Topology, supervised by Arend

Heyting, and defended in 1966. A one-year leave in 1966-1967 at Stanford, where his host was Georg Kreisel, was perhaps his second most formative experience, for both the topics and the convictions behind his main line of work, the formal metamathematics of intuitionistic mathematics. This influence was first seen in Troelstra's widely-read Principles of Intuitionism of 1969, which originated in a lecture series he had given at the Summer Conference on Proof Theory and Intuitionism, Buffalo, NY, in 1968.

In 1970 Troelstra succeeded Heyting as full professor, and he remained at the University of Amsterdam until his retirement in 2000. Over the years, his work naturally became somewhat more diverse, and in particular he increasingly wrote also on the history and philosophy of intuitionism (and of constructive mathematics in general).

Another scientific and leisure interest of his was botany, which extended to accounts of journeys made to investigate natural history (botany, zoology, mineralogy, geology). This led to three books in Dutch, as well as the voluminous Bibliography of Natural History Travel Narratives.

Besides the Académie Internationale de Philosophie des Sciences, he was an elected member of the Royal Dutch Academy of Sciences (1976) and corresponding member of the Bavarian Academy of Sciences (1996).

In 1996 the Technische Universität München awarded him the F.L. Bauer prize for internationally outstanding contributions to theoretical computer science, citing his contributions to making intuitionistic logic useful in extracting algorithms and programs from mathematical proofs.

Troelstra's scientific archive is kept at the Noord-Hollands Archief in Haarlem.

His was a stern, ironical, and very scientific mind.

Principal publications:

- Principles of Intuitionism (Lecture Notes in Mathematics 95,Heidelberg: Springer, 1969)

- (with Georg Kreisel) Formal systems for some branches of intuitionistic analysis (Annals of Mathematical Logic, 1 (1970),

229-387)

- (with Jeff Zucker, Craig Smorynski, and William Howard) Metamathematical Investigations of Intuitionistic Arithmetic and

Analysis (Lecture Notes in Mathematics 344, Heidelberg: Springer, 1973)

- Analyzing choice sequences, Journal of Philosophical Logic 12 (1983), 197-260.

- (with Jane Kister and Dirk van Dalen) Omega-Bibliography of mathematical Logic. Vol. VI: Proof Theory and Constructive Mathematics (Heidelberg: Springer, 1987)

- (with Dirk van Dalen) Constructivism in Mathematics (Amsterdam:Elsevier, 1988, 2 volumes)

- (with Helmut Schwichtenberg) Basic Proof Theory (Cambridge Uiversity Press, 1996)

- Bibliography of Natural History Travel Narratives (Leiden: Brill, 2016)