+/** Expose this object's derivative structure.
+ *
+ * Parameter numbers occurring more than once stand for repeated
+ * differentiation with respect to that parameter. If a symbolic function
+ * f(x,y) is differentiated with respect to x, this method will return {0}.
+ * If f(x,y) is differentiated twice with respect to y, it will return {1,1}.
+ * (This corresponds to the way this object is printed.)
+ *
+ * @return multiset of function's parameter numbers that are abstractly
+ * differentiated. */
+const paramset& fderivative::derivatives() const
+{
+ return parameter_set;
+}
+
+