diff --git a/src/HOL/Library/NList.thy b/src/HOL/Library/NList.thy
--- a/src/HOL/Library/NList.thy
+++ b/src/HOL/Library/NList.thy
@@ -1,101 +1,104 @@
 (* Author:     Tobias Nipkow
     Copyright   2000 TUM
 *)
 
 section \<open>Fixed Length Lists\<close>
 
 theory NList
 imports Main
 begin
 
 definition nlists :: "nat \<Rightarrow> 'a set \<Rightarrow> 'a list set"
   where "nlists n A = {xs. size xs = n \<and> set xs \<subseteq> A}"
 
 lemma nlistsI: "\<lbrakk> size xs = n; set xs \<subseteq> A \<rbrakk> \<Longrightarrow> xs \<in> nlists n A"
   by (simp add: nlists_def)
 
-lemma nlistsE_length (*rm simp del*): "xs \<in> nlists n A \<Longrightarrow> size xs = n"
+text \<open>These [simp] attributes are double-edged.
+ Many proofs in Jinja rely on it but they can degrade performance.\<close>
+
+lemma nlistsE_length [simp]: "xs \<in> nlists n A \<Longrightarrow> size xs = n"
   by (simp add: nlists_def)
 
 lemma less_lengthI: "\<lbrakk> xs \<in> nlists n A; p < n \<rbrakk> \<Longrightarrow> p < size xs"
-by (simp add: nlistsE_length)
+by (simp)
 
-lemma nlistsE_set[simp](*rm simp del*): "xs \<in> nlists n A \<Longrightarrow> set xs \<subseteq> A"
+lemma nlistsE_set[simp]: "xs \<in> nlists n A \<Longrightarrow> set xs \<subseteq> A"
 unfolding nlists_def by (simp)
 
 lemma nlists_mono:
 assumes "A \<subseteq> B" shows "nlists n A \<subseteq> nlists n B"
 proof
   fix xs assume "xs \<in> nlists n A"
-  then obtain size: "size xs = n" and inA: "set xs \<subseteq> A" by (simp add:nlistsE_length)
+  then obtain size: "size xs = n" and inA: "set xs \<subseteq> A" by (simp)
   with assms have "set xs \<subseteq> B" by simp
   with size show "xs \<in> nlists n B" by(clarsimp intro!: nlistsI)
 qed
 
 lemma nlists_n_0 [simp]: "nlists 0 A = {[]}"
 unfolding nlists_def by (auto)
 
 lemma in_nlists_Suc_iff: "(xs \<in> nlists (Suc n) A) = (\<exists>y\<in>A. \<exists>ys \<in> nlists n A. xs = y#ys)"
 unfolding nlists_def by (cases "xs") auto
 
 lemma Cons_in_nlists_Suc [iff]: "(x#xs \<in> nlists (Suc n) A) \<longleftrightarrow> (x\<in>A \<and> xs \<in> nlists n A)"
 unfolding nlists_def by (auto)
 
 lemma nlists_not_empty: "A\<noteq>{} \<Longrightarrow> \<exists>xs. xs \<in> nlists n A"
 by (induct "n") (auto simp: in_nlists_Suc_iff)
 
 
 lemma nlistsE_nth_in: "\<lbrakk> xs \<in> nlists n A; i < n \<rbrakk> \<Longrightarrow> xs!i \<in> A"
 unfolding nlists_def by (auto)
 
 lemma nlists_Cons_Suc [elim!]:
   "l#xs \<in> nlists n A \<Longrightarrow> (\<And>n'. n = Suc n' \<Longrightarrow> l \<in> A \<Longrightarrow> xs \<in> nlists n' A \<Longrightarrow> P) \<Longrightarrow> P"
 unfolding nlists_def by (auto)
 
 lemma nlists_appendE [elim!]:
   "a@b \<in> nlists n A \<Longrightarrow> (\<And>n1 n2. n=n1+n2 \<Longrightarrow> a \<in> nlists n1 A \<Longrightarrow> b \<in> nlists n2 A \<Longrightarrow> P) \<Longrightarrow> P"
 proof -
   have "\<And>n. a@b \<in> nlists n A \<Longrightarrow> \<exists>n1 n2. n=n1+n2 \<and> a \<in> nlists n1 A \<and> b \<in> nlists n2 A"
     (is "\<And>n. ?list a n \<Longrightarrow> \<exists>n1 n2. ?P a n n1 n2")
   proof (induct a)
     fix n assume "?list [] n"
     hence "?P [] n 0 n" by simp
     thus "\<exists>n1 n2. ?P [] n n1 n2" by fast
   next
     fix n l ls
     assume "?list (l#ls) n"
     then obtain n' where n: "n = Suc n'" "l \<in> A" and n': "ls@b \<in> nlists n' A" by fastforce
     assume "\<And>n. ls @ b \<in> nlists n A \<Longrightarrow> \<exists>n1 n2. n = n1 + n2 \<and> ls \<in> nlists n1 A \<and> b \<in> nlists n2 A"
     from this and n' have "\<exists>n1 n2. n' = n1 + n2 \<and> ls \<in> nlists n1 A \<and> b \<in> nlists n2 A" .
     then obtain n1 n2 where "n' = n1 + n2" "ls \<in> nlists n1 A" "b \<in> nlists n2 A" by fast
     with n have "?P (l#ls) n (n1+1) n2" by simp
     thus "\<exists>n1 n2. ?P (l#ls) n n1 n2" by fastforce
   qed
   moreover assume "a@b \<in> nlists n A" "\<And>n1 n2. n=n1+n2 \<Longrightarrow> a \<in> nlists n1 A \<Longrightarrow> b \<in> nlists n2 A \<Longrightarrow> P"
   ultimately show ?thesis by blast
 qed
 
 
 lemma nlists_update_in_list [simp, intro!]:
   "\<lbrakk> xs \<in> nlists n A; x\<in>A \<rbrakk> \<Longrightarrow> xs[i := x] \<in> nlists n A"
   by (metis length_list_update nlistsE_length nlistsE_set nlistsI set_update_subsetI)
 
 lemma nlists_appendI [intro?]:
   "\<lbrakk> a \<in> nlists n A; b \<in> nlists m A \<rbrakk> \<Longrightarrow> a @ b \<in> nlists (n+m) A"
 unfolding nlists_def by (auto)
 
 lemma nlists_append:
   "xs @ ys \<in> nlists k A \<longleftrightarrow>
    k = length(xs @ ys) \<and> xs \<in> nlists (length xs) A \<and> ys \<in> nlists (length ys) A"
 unfolding nlists_def by (auto)
 
 lemma nlists_map [simp]: "(map f xs \<in> nlists (size xs) A) = (f ` set xs \<subseteq> A)"
 unfolding nlists_def by (auto)
 
 lemma nlists_replicateI [intro]: "x \<in> A \<Longrightarrow> replicate n x \<in> nlists n A"
  by (induct n) auto
 
 lemma nlists_set[code]: "nlists n (set xs) = set (List.n_lists n xs)"
 unfolding nlists_def by (rule sym, induct n) (auto simp: image_iff length_Suc_conv)
 
 end