12 lines
286 B
Text
12 lines
286 B
Text
import data.list
|
|
open list
|
|
|
|
variable {T : Type}
|
|
|
|
theorem append.assoc : ∀ (s t u : list T), s ++ t ++ u = s ++ (t ++ u)
|
|
| append.assoc nil t u := by esimp
|
|
| append.assoc (a :: l) t u :=
|
|
begin
|
|
change a :: (l ++ t ++ u) = (a :: l) ++ (t ++ a),
|
|
rewrite append.assoc
|
|
end
|