+/*----- Helpful field operations ------------------------------------------*/
+
+/* --- @field_id@ --- *
+ *
+ * Arguments: @field *f@ = pointer to a field
+ * @mp *d@ = a destination element
+ * @mp *x@ = a source element
+ *
+ * Returns: The result element.
+ *
+ * Use: An identity operation which can be used if your field has no
+ * internal representation.
+ */
+
+extern mp *field_id(field */*f*/, mp */*d*/, mp */*x*/);
+