have h2 := calc f^[r] b
    = a := fab1
  _ = f^[r] a := (h1 r).symm
f : ℕ+ → ℕ+
hf : ∀ (n : ℕ+), f^[↑(f n)] n * f (f n) = n ^ 2
a b : ℕ+
r : ℕ
fab1 : f^[r] b = a
fab2 : f a = a
h1 : ∀ (s : ℕ), f^[s] a = a
⊢ b = a
f : ℕ+ → ℕ+
hf : ∀ (n : ℕ+), f^[↑(f n)] n * f (f n) = n ^ 2
a b : ℕ+
r : ℕ
fab1 : f^[r] b = a
fab2 : f a = a
h1 : ∀ (s : ℕ), f^[s] a = a
h2 : f^[r] b = f^[r] a
⊢ b = a