  This paper shows how the Theorem of Residues (TR) and the Gelfand-Fuchs
cocycle can be deduced in a simple way from the Weil Reciprocity Law (WRL).
Indeed, if one understand WRL as the triviality of certain extension of groups,
then TR is the same statement at the level of Lie algebras. Finally, the
Gelfand-Fuchs cocycle can also be obtained in this way.
