diff --git a/thiele.lisp b/thiele.lisp
index 7775224..e42cd96 100644
--- a/thiele.lisp
+++ b/thiele.lisp
@@ -52,6 +52,17 @@
 ; (%i3) keepfloat:true$
 ; (%i4) subst(x=0.5, thiele(b,a))*3;
 ; (%o4)                         3.14159265357928
+;
+;    The function may be used with exact values, but it is highly sensitive
+;    to input values, and equally spaced abscissæ often yield some division
+;    by zero error.
+;
+; (%i5) thiele([1,2,5,6], [10,12,11,13]);
+;                                   2
+;                                9 x  + 29 x - 238
+; (%o5)                          -----------------
+;                                    8 x - 28
+
 
 (defun $thiele (u v)
   (loop for rh on