The 2025 Alonzo Church Award for Outstanding Contributions to Logic and Computation is presented to **Paul Blain Levy** for his fundamental study of effectful λ-calculi through the Call-by-Push-Value calculus. The awardee book and paper are: > Paul Blain Levy. Call-By-Push-Value: A Functional/Imperative Synthesis. Semantics Structures in Computation 2, Springer 2004, ISBN 1-4020-1730-8 > > Paul Blain Levy. Call-by-Push-Value: Decomposing call-by-value and call-by-name. High.-Order Symb. Comput. 19(4): 377-414 (2006) ## The Contribution Initiated by Alonzo Church, the research programme into the λ-calculus as an abstract model of computation has spurred volumes of fundamental research in logic and computation. By the end of the 20th century, the studies of the λ-calculus in its purely logical form and its applied effectful form bifurcated. In an outstanding contribution, Levy has reunited the many existing research streams into the study of one subsuming calculus: Call-by-Push-Value (CBPV). Levy developed and presented an extraordinarily large body of evidence spanning a cross-section of the semantic theory of the λ-calculus and its application to programming language modelling, including: algebraic datatypes, operational semantics, denotational semantics, and equational theories. To date, CBPV remains a unifying starting point in the study of computational and logical phenomena, including: effects, polarisation, term normalisation, type-isomorphisms, and program transformations. In addition to its scientific contribution, the nominated monograph is a unique access-point into the culmination of decades of logic and programming language semantics.

The category fat Delta, introduced by J. Kock, is a modification of the simplex category where the degeneracies behave weakly. The objective of this note is to provide tools for working with fat Delta. In particular, we identify three types of morphisms: degenerated, standard and vertical faces, and establish six relations between these classes. We then show that fat Delta is generated by these morphisms and relations.

ESSLLI 2025