Fix hyperlinks in the documentation of symbolic functions (trac 24398)

Author: egourgoulhon

src/doc/en/reference/calculus/index.rst

@@ -1,3 +1,5 @@
+.. _symbolic-calculus:
+
 Symbolic Calculus
 =================
 

src/doc/en/reference/functions/index.rst

@@ -1,3 +1,6 @@
+.. _special-functions:
+
+
 Functions
 =========
 
@@ -28,7 +31,7 @@ Built-in Functions
    sage/functions/min_max
 
 Please find extensive developer documentation for creating new functions
-in the :doc:`Symbolic Calculus module<calculus/index>`, in particular in
-:doc:`sage/symbolic/function`.
+in :ref:`symbolic-calculus`, in particular in the section
+:ref:`Classes for symbolic functions <symbolic-function-classes>`.
 
 .. include:: ../footer.txt

src/sage/symbolic/function.pyx

@@ -1,11 +1,13 @@
 r"""
 Classes for symbolic functions
 
+.. _symbolic-function-classes:
+
 To enable their usage as part of symbolic expressions, symbolic function
 classes are derived from one of the subclasses of :class:`Function`:
 
  * :class:`BuiltinFunction`: the code of these functions is written in Python;
-   many special functions are of this type, see this :doc:`list <functions/index>`
+   many :ref:`special functions<special-functions>` are of this type
  * :class:`GinacFunction`: the code of these functions is written in C++ and
    part of the Pynac support library; most elementary functions are of this type
  * :class:`SymbolicFunction`: symbolic functions defined on the Sage command