diff --git a/README.md b/README.md
index e2405c4..f513df9 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,3 @@ It requires Tcl/Tk 8.6+.
 
 ## 3. Library list
 - lSum/lSum.tcl (Yuji SODE, 2018): https://gist.github.com/YujiSODE/1f9a4e2729212691972b196a76ba9bd0
-
-## 4. Reference
-- Iri, M. and Fujino., Y. 1985. Suchi keisan no joshiki (Japanese). Kyoritsu Shuppan Co., Ltd. ISBN 978-4-320-01343-8