--- checklinks.awk.original	2014-11-17 11:31:40.000000000 -0800
+++ checklinks.awk	2015-09-14 18:14:38.387950158 -0700
@@ -2,7 +2,14 @@
 
 # Contributed by Paul Eggert.
 
-/^Link/ { used[$2] = 1 }
+/^Link/ { 
+	if(linkDefined[$3] != "")
+	{
+		printf "%s: Link previously defined\n", $3
+	}
+	used[$2] = 1 
+	linkDefined[$3] = $2
+}
 /^Zone/ { defined[$2] = 1 }
 
 END {