The Euler Characteristic of a Formula in Godel Logic

Using the lattice-theoretic version of the Euler characteristic introduced by V. Klee and G.-C. Rota, we define the Euler characteristic of a formula in Gödel logic (over finitely or infinitely many truth-values). We then prove that the information encoded by the Euler characteristic is classical, i.e., coincides with the analogous notion defined over Boolean logic. Building on this, we define k-valued versions of the Euler characteristic of a formula φ, for each integer k ≥ 2, and prove that they indeed provide information about the logical status of φ in Gödel k-valued logic. Specifically, our main result shows that the k-valued Euler characteristic is an invariant that separates k-valued tautologies from non-tautologies.