s n : Nat
⊢ reverse [s + n] ++ reverse (range' s n) = (s + n - 0) :: map ((fun x => s + n - x) ∘ succ) (range n)
s n : Nat
⊢ reverse (range' s (n + 1)) = map (fun x => s + (n + 1) - 1 - x) (range (n + 1))
rw [range'_1_concat, reverse_append, range_succ_eq_map,
  show s + (n + 1) - 1 = s + n from rfl, map, map_map]
s n : Nat
⊢ map (fun x => s + n - x - 1) (range n) = map ((fun x => s + n - x) ∘ succ) (range n)
s n : Nat
⊢ reverse [s + n] ++ reverse (range' s n) = (s + n - 0) :: map ((fun x => s + n - x) ∘ succ) (range n)
simp [reverse_range', Nat.sub_right_comm]
no goals
s n : Nat
⊢ map (fun x => s + n - x - 1) (range n) = map ((fun x => s + n - x) ∘ succ) (range n)
rfl