*Flavien Breuvart*

**On the characterization of models of H***ABSTRACT. We give a characterization, with respect to a large class of models of untyped lambda-calculus, of those models which are fully abstract for head normalization, i.e., whose equational theory is H*. An extensional K-model D is fully abstract if and only if it is hyperimmune, i.e., non-well founded chains of elements of D cannot be captured by any recursive function.

*Yaron Velner*

**Finite-Memory Strategy Synthesis for Robust Multidimensional Mean-Payoff Objectives**ABSTRACT. Two-player games on graphs provide the mathematical foundation for the study of reactive systems. In the quantitative framework, an objective assigns a value to every play, and the goal of player 1 is to minimize the value of the objective. In this framework, there are two relevant synthesis problems to consider: the quantitative analysis problem is to compute the minimal (or infimum) value that player 1 can assure, and the boolean analysis problem asks whether player 1 can assure that the value of the objective is at most r (for a given threshold r). Mean-payoff expression games are played on a multidimensional weighted graph. An atomic mean-payoff expression objective is the mean-payoff value (the long-run average weight) of a certain dimension, and the class of mean-payoff expressions is the closure of atomic mean-payoff expressions under the algebraic operations of max, min, numerical complement and sum. In this work, we study for the first time the strategy synthesis problems for games with robust quantitative objectives, namely, games with mean-payoff expression objectives. While in general, optimal strategies for these games require infinite-memory, in synthesis we are typically interested in the construction of a finite-state system. Hence, we consider games in which player 1 is restricted to finite-memory strategies, and our main contribution is as follows. We prove that for mean-payoff expressions, the quantitative analysis problem is computable, and the boolean analysis problem is inter-reducible with Hilbert's tenth problem over rationals - a fundamental long-standing open problem in computer science and mathematics.