diff --git a/src/pg/sql/12_contour2.sql b/src/pg/sql/12_contour2.sql
index 9b07d92..f9e37d8 100644
--- a/src/pg/sql/12_contour2.sql
+++ b/src/pg/sql/12_contour2.sql
@@ -178,6 +178,7 @@ BEGIN
 
     running_merge := running_merge || ST_ExteriorRing(ST_Convexhull(ST_Collect(geomin))) ;
 
+    -- multilines version
     WITH
     a as(
      SELECT unnest(running_merge) as geo