+ *
+ * N.B.
+ *
+ * 1. The function don't have to return a (GiNaC) function or class, it
+ * can return any expression.
+ * 2. Overloaded functions/ctors are paritally supported, i.e. there might
+ * be several functions with the same name, but they should take different
+ * number of arguments.
+ * 3. User can extend the parser via custom prototype tables. It's possible
+ * to read user defined classes, create abbreviations, etc.
+ *
+ * NOTE: due to a hack that allows user defined functions to be parsed, the map
+ * value of type reader_func is internally treated as an unsigned and not as a
+ * function pointer!! The unsigned has to correspond to the serial number of
+ * the defined GiNaC function.