+extern const unsigned function_index_zeta1;
+inline function zeta(const ex & p1) {
+ return function(function_index_zeta1, p1);
+}
+/** Derivatives of Riemann's Zeta-function. */
+extern const unsigned function_index_zeta2;
+inline function zeta(const ex & p1, const ex & p2) {
+ return function(function_index_zeta2, p1, p2);
+}