diff --git a/src/util/sum.scad b/src/util/sum.scad
index 0384c9fc..c2e5c1be 100644
--- a/src/util/sum.scad
+++ b/src/util/sum.scad
@@ -1,3 +1,13 @@
+/**
+* sum.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-sum.html
+*
+**/ 
+
 use <_impl/_sum_impl.scad>;
 
 function sum(lt) = _sum_impl(lt, len(lt));
\ No newline at end of file