diff --git a/report/references.bib b/report/references.bib
index 6ba45dc..472849f 100644
--- a/report/references.bib
+++ b/report/references.bib
@@ -24,3 +24,11 @@
   url = "http://opensource.org/licenses/Zlib",
   urldate = "2015-03-12"
 }
+
+@online{spline,
+    author="Jana Proch\'azkov\'a",
+    title="DERIVATIVE OF B-SPLINE FUNCTION",
+    url="http://mat.fsv.cvut.cz/gcg/sbornik/prochazkova.pdf",
+    urldate="2015-03-12"
+}
+
diff --git a/report/subsections/splines.tex b/report/subsections/splines.tex
index 91750d3..f0a79df 100644
--- a/report/subsections/splines.tex
+++ b/report/subsections/splines.tex
@@ -35,3 +35,5 @@ The \texttt{prime} member function computes the derivative like this
 $$C'(t) = \sum_{i=0}^m N_i^{\prime n} (t) P_i $$
 with
 $$ N_i^{\prime n}(t) = \frac{n}{t_{i+n}-t_{i}}N_i^{n-1}(t) - \frac{n}{t_{i+n+1}-t_{i+1}}N_{i+1}^{n-1}(t)$$
+
+These formulas have been taken from the reference \cite{spline}.