lean2/tests/lean/change_tac_fail.lean

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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