We are sad to report that Solomon Feferman died on 26 July 2016 following a stroke. Sol is widely known among mathematicians, philosophers, and computer scientists for his contributions to many areas in mathematical logic and the philosophy of logic and mathematics. He provided the foundations for generalizations of the Gödel incompleteness theorems and the arithmetization and formalisation of metamathematics in general. He shaped modern proof theory; in particular in ordinal analysis he determined the proof-theoretic ordinal of the predicative subsystem, known as the Schütte–Feferman ordinal. Building on earlier work by Turing, he proved results on iterated additions of proof-theoretic reflection principles to arithmetic. Sol’s work on axiomatic theories of truth and, in particular, the Kripke-Feferman system has been highly influential.

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