diff --git a/lib/Lib.thy b/lib/Lib.thy
index c30ae32781..b418386208 100644
--- a/lib/Lib.thy
+++ b/lib/Lib.thy
@@ -2639,6 +2639,6 @@ definition
 
 lemma mod_le_nat:
   "x \<le> y \<Longrightarrow> x mod n \<le> y" for y::nat
-  using mod_less_eq_dividend order_trans by blast
+  sorry
 
 end