Safety Signature for Geometric Constructions Shahar Lev (TAU) Abstract: This is a part of an on-going project aiming at getting a unified theory of constructions as they are used in different branches of Mathematics. Taking a purely logical view, such a unification has previously been achieved of the notion of computability used in recursion theory and the set-theoretical notion of constructibility. This was done by using the notion of safety signature - a generalization of the usual notion of a first-order signature in which constructibility and decidability issues are taken into account. In this talk we use Tarski's formalization of Euclidean Geometry in order to characterize within a similar strictly syntactical framework the oldest type of constructions studied in mathematics: Euclidean ruler and compass constructions. Joint work with Arnon Avron.