CONTRIBUTORS

--- a/CONTRIBUTORS	Sat Oct 21 18:19:11 2017 +0200
+++ b/CONTRIBUTORS	Sun Oct 22 09:10:10 2017 +0200
@@ -6,6 +6,8 @@
 Contributions to this Isabelle version
 --------------------------------------
 
+* October 2017: Alexander Maletzky
+  Derivation of axiom "iff" in HOL.thy from the other axioms.
 
 Contributions to Isabelle2017
 -----------------------------