On the Decomposition of the Small Diagonal of a K3 Surface

Abstract: We give a new proof of the theorem of Beauville and Voisin about the decomposition of the small diagonal of a K3 surface S. Our proof is explicit and works with the embedding of S in a projective space. It is different from the one used by Beauville and Voisin, which employed the existence of one-parameters families of elliptic curves.