-are not already existing. Add edges between every two nodes
-corresponding to a pair of successive modules in the arguments.
+have not been already added in a previous call. Add edges between
+every two nodes associated to two successive modules in the
+arguments.
+
+Calling this function with n > 2 arguments is strictly equivalent to
+calling it n-1 times on the pairs of successive arguments.
+
+Accepting more than two arguments allows in particular to add
+anonymous modules, which are not associated to variables. In principle
+the only ones that have to be non-anonymous are those that have more
+than one successor / predecessor and/or are inputs / outputs.