The EATCS Award for the best theory paper at ETAPS 2026 was awarded to Isa Vialard, Joël Ouaknine and Quentin Guilmant for their paper "The value problem for weighted timed games with two clocks is undecidable", published in FoSSaCS 2026. The EATCS award is given each year to the best ETAPS papers in theoretical computer science.

The paper solves a long-standing open problem in the field of quantitative games. Weighted timed games were introduced in several works in the early 2000s, and constitute a fundamental model for formal verification and control. The key decision problems for quantitative games are the existence of winning strategies and the ‘value problem’: is the inf-sup across all pairs of Minimizer/Maximizer strategies smaller than a given rational? With three clocks, the value problem was proved undecidable in 2015. With a single clock, the problem was shown to be decidable in 2022. This paper finally closes the gap: with two clocks, both problems are shown to be undecidable using a novel and ingenious reduction, resulting in a deep contribution

MPI-SWS scientific director Joël Ouaknine was appointed as a Fellow by the European Association for Theoretical Computer Science (EATCS). Joël, who leads the “Foundations of Algorithmic Verification” research group, was appointed EATCS fellow for "fundamental contributions to the algorithmic analysis of dynamical systems and related formalisms."

The EATCS Fellows Program was established by the association in 2014 to recognize outstanding EATCS members for their scientific achievements in the field of Theoretical Computer Science.

Further Information: 

• https://eatcs.org/index.php/component/content/article/1-news/3028--eatcs-fellows-class-of-2026-named
• https://www.eatcs.org/index.php/eatcs-fellows