--- a/src/HOL/Library/Extended_Nat.thy Wed Feb 13 02:13:46 2019 +0100
+++ b/src/HOL/Library/Extended_Nat.thy Wed Feb 13 07:48:42 2019 +0100
@@ -531,7 +531,7 @@
lemma enat_add_left_cancel_less: "a + b < a + c \<longleftrightarrow> a \<noteq> (\<infinity>::enat) \<and> b < c"
unfolding plus_enat_def by (simp split: enat.split)
-lemma plus_eq_infty_iff_enat[simp]: "(m::enat) + n = \<infinity> \<longleftrightarrow> m=\<infinity> \<or> n=\<infinity>"
+lemma plus_eq_infty_iff_enat: "(m::enat) + n = \<infinity> \<longleftrightarrow> m=\<infinity> \<or> n=\<infinity>"
using enat_add_left_cancel by fastforce
ML \<open>