--- a/thys/Abacus.thy	Fri Dec 21 15:30:24 2018 +0100
+++ b/thys/Abacus.thy	Mon Jan 07 13:44:19 2019 +0100
@@ -1,5 +1,6 @@
 (* Title: thys/Abacus.thy
    Author: Jian Xu, Xingyuan Zhang, and Christian Urban
+   Modifications: Sebastiaan Joosten
 *)
 
 chapter {* Abacus Machines *}