--- a/src/HOL/List.thy Wed May 01 10:40:40 2019 +0000
+++ b/src/HOL/List.thy Wed May 01 10:40:42 2019 +0000
@@ -2678,6 +2678,26 @@
from this that show ?thesis by fastforce
qed
+lemma zip_eq_Nil_iff:
+ "zip xs ys = [] \<longleftrightarrow> xs = [] \<or> ys = []"
+ by (cases xs; cases ys) simp_all
+
+lemma zip_eq_ConsE:
+ assumes "zip xs ys = xy # xys"
+ obtains x xs' y ys' where "xs = x # xs'"
+ and "ys = y # ys'" and "xy = (x, y)"
+ and "xys = zip xs' ys'"
+proof -
+ from assms have "xs \<noteq> []" and "ys \<noteq> []"
+ using zip_eq_Nil_iff [of xs ys] by simp_all
+ then obtain x xs' y ys' where xs: "xs = x # xs'"
+ and ys: "ys = y # ys'"
+ by (cases xs; cases ys) auto
+ with assms have "xy = (x, y)" and "xys = zip xs' ys'"
+ by simp_all
+ with xs ys show ?thesis ..
+qed
+
lemma pair_list_eqI:
assumes "map fst xs = map fst ys" and "map snd xs = map snd ys"
shows "xs = ys"