diff --git a/library/data/list/basic.lean b/library/data/list/basic.lean index ded9ea279e..5654a45cab 100644 --- a/library/data/list/basic.lean +++ b/library/data/list/basic.lean @@ -447,11 +447,6 @@ end /- nth element -/ section nth -definition nth : list T → nat → option T -| [] n := none -| (a :: l) 0 := some a -| (a :: l) (n+1) := nth l n - theorem nth_zero [simp] (a : T) (l : list T) : nth (a :: l) 0 = some a := rfl diff --git a/library/init/list.lean b/library/init/list.lean index 73ace3e8a6..67fe278605 100644 --- a/library/init/list.lean +++ b/library/init/list.lean @@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE. Author: Leonardo de Moura -/ prelude -import init.logic +import init.logic init.nat open decidable list protected definition list.is_inhabited [instance] (A : Type) : inhabited (list A) := @@ -42,4 +42,11 @@ definition length : list A → nat | [] := 0 | (a :: l) := length l + 1 +open option nat + +definition nth : list A → nat → option A +| [] _ := none +| (a :: l) 0 := some a +| (a :: l) (n+1) := nth l n + end list