diff --git a/Common/util_eddies.py b/Common/util_eddies.py
index 2dabadbfdfb15a676744291c81d19293f4597c26..734e18050531795fabdd4f250e1c6b97e3c49466 100644
--- a/Common/util_eddies.py
+++ b/Common/util_eddies.py
@@ -95,6 +95,11 @@ class SHPC_class:
         return self._n_dates[i_slice]
 
     def get_ishape_last(self, i_slice, orientation):
+        """Can return None if ishape_last.txt does not exist and cannot be
+        created.
+
+        """
+
         if self._ishape_last[i_slice][orientation] is None:
             fname = path.join(self.dir, f"Slice_{i_slice}", orientation,
                               "ishape_last.txt")
@@ -140,6 +145,8 @@ class SHPC_class:
         return self._n_shapes[i_slice][orientation]
 
     def _create_ishape_last(self, i_slice, orientation):
+        """Can fail if it cannot get a reader."""
+
         last_date = self.d_init[i_slice]
         date_ishape = [] # list of tuples (date, ishape)
         reader = self.get_reader(i_slice, "extremum", orientation)
diff --git a/Inst_eddies/Documentation_texfol/documentation.tex b/Inst_eddies/Documentation_texfol/documentation.tex
index 39a9ae86249ca7968e8813884ba0fda72b8d5c72..bae4f3bd0e362077ca00a34c1ae9372fb9cbd4b2 100644
--- a/Inst_eddies/Documentation_texfol/documentation.tex
+++ b/Inst_eddies/Documentation_texfol/documentation.tex
@@ -249,8 +249,12 @@ index of the array be a date present in the slice. We have :
 \begin{equation*}
   l(d) = \sum_{d' = d_0} ^d e_\mathrm{max}(d') - 1
 \end{equation*}
-$e_\mathrm{max}(d) = 0$ if $d$ is not in the slice. So the shape index
-$i$ of the eddy with eddy index $e$ at date $d$ is:
+$e_\mathrm{max}(d) = 0$ if $d$ is not in the slice. So, if;
+\begin{equation*}
+  1 \le e \le e_\mathrm{max}(d)
+\end{equation*}
+then the shape index $i$ of the eddy with eddy index $e$ at date $d$
+is:
 \begin{equation*}
   i =
   \begin{array}{|ll}