suffices m ≤ k
  from Nat.succ_le_succ (div_le_div this)
m : Nat
h_ind : ∀ {n : Nat}, m / 2 + 1 ≤ n → log2' (m / 2 + 1) ≤ log2' n
n : Nat
h : m + 2 ≤ n
k : Nat := n - 2
this : n = k + 2
⊢ m / 2 + 1 ≤ k / 2 + 1
m : Nat
h_ind : ∀ {n : Nat}, m / 2 + 1 ≤ n → log2' (m / 2 + 1) ≤ log2' n
n : Nat
h : m + 2 ≤ n
k : Nat := n - 2
this : n = k + 2
⊢ m ≤ k