Geometry in the Spring A mini-conference on geometry in Ben Gurion University of the Negev Abstracts Sergey Fomin (University of Michigan, Ann Arbor), Cluster Transformations. Cluster transformations Cluster transformations are a surprisingly ubiquitous family of algebraic recurrences. They arise in diverse mathematical contexts, from representation theory and enumerative combinatorics to mathematical physics and classical geometry (Euclidean, spherical, or hyperbolic). I will present some of the most basic and concrete examples of cluster transformations, and briefly discuss their remarkable properties such as periodicity, integrability, Laurentness, and positivity. Eugenii Shustin (Tel Aviv University), Refined enumerative tropical geometry Abstract: We overview the new direction in tropical geometry - the refined enumerative tropical geometry, which was initiated by F. Block and L Goettsche about four years ago. The main issue is the existence of tropical enumerative invariants that are not numbers but functions interpolating between the complex and real enumerative invariants. We show several examples of the refined count of tropical curves and discuss open problems, among them the most challenging one - search for a possible algebraic-geometric counterpart of the refined tropical enumerative invariants. Ran Tessler (Weizmann Institute of Science), The open Arf invariant and stratifications of moduli spaces of surfaces with boundary. Abstract: We consider the moduli space of marked surfaces with boundary. We show a stratification of it using real Strebel-Jenkins differentials. We then explain the notion of graded spin structures (defined in a joint work with J. Solomon) and show that the moduli of graded spin surfaces can be stratified using a decoration of the spinless stratification. We use this decoration to find, for each stratum of highest dimension, an orientation expression. These expressions turn out to be invariant to cluster-like moves, and we use this to deduce that the graded spin moduli is orientable.