diff -r 7929240e44d4 -r e4e57da0583a src/HOL/Library/Sublist.thy
--- a/src/HOL/Library/Sublist.thy	Wed Feb 14 11:51:03 2018 +0100
+++ b/src/HOL/Library/Sublist.thy	Wed Feb 14 16:32:09 2018 +0100
@@ -147,6 +147,9 @@
 lemma filter_mono_prefix: "prefix xs ys \<Longrightarrow> prefix (filter P xs) (filter P ys)"
 by (auto simp: prefix_def)
 
+lemma sorted_antimono_prefix: "prefix xs ys \<Longrightarrow> sorted ys \<Longrightarrow> sorted xs"
+by (metis sorted_append prefix_def)
+
 lemma prefix_length_less: "strict_prefix xs ys \<Longrightarrow> length xs < length ys"
   by (auto simp: strict_prefix_def prefix_def)
 
@@ -526,6 +529,9 @@
 lemma set_mono_suffix: "suffix xs ys \<Longrightarrow> set xs \<subseteq> set ys"
 by (auto simp: suffix_def)
 
+lemma sorted_antimono_suffix: "suffix xs ys \<Longrightarrow> sorted ys \<Longrightarrow> sorted xs"
+by (metis sorted_append suffix_def)
+
 lemma suffix_ConsD2: "suffix (x # xs) (y # ys) \<Longrightarrow> suffix xs ys"
 proof -
   assume "suffix (x # xs) (y # ys)"