n : ℕ
⊢ fib n * (2 * fib (n + 1) - fib n) + (fib (n + 1) ^ 2 + fib n ^ 2) = fib (n + 1) * (2 * fib n + fib (n + 1))
n : ℕ
⊢ fib (2 * n + 2) = fib (n + 1) * (2 * fib n + fib (n + 1))
rw [fib_add_two, fib_two_mul, fib_two_mul_add_one]
n : ℕ
this : fib n ≤ 2 * fib (n + 1)
⊢ fib n * (2 * fib (n + 1) - fib n) + (fib (n + 1) ^ 2 + fib n ^ 2) = fib (n + 1) * (2 * fib n + fib (n + 1))
n : ℕ
⊢ fib n * (2 * fib (n + 1) - fib n) + (fib (n + 1) ^ 2 + fib n ^ 2) = fib (n + 1) * (2 * fib n + fib (n + 1))
have : fib n ≤ 2 * fib (n + 1) :=
  le_trans (fib_le_fib_succ) (mul_comm 2 _ ▸ le_mul_of_pos_right two_pos)
n : ℕ
this : fib n ≤ 2 * fib (n + 1)
⊢ ↑(fib n) * (2 * ↑(fib (n + 1)) - ↑(fib n)) + (↑(fib (n + 1)) ^ 2 + ↑(fib n) ^ 2) =
    ↑(fib (n + 1)) * (2 * ↑(fib n) + ↑(fib (n + 1)))
n : ℕ
this : fib n ≤ 2 * fib (n + 1)
⊢ fib n * (2 * fib (n + 1) - fib n) + (fib (n + 1) ^ 2 + fib n ^ 2) = fib (n + 1) * (2 * fib n + fib (n + 1))
zify [this]
no goals
n : ℕ
this : fib n ≤ 2 * fib (n + 1)
⊢ ↑(fib n) * (2 * ↑(fib (n + 1)) - ↑(fib n)) + (↑(fib (n + 1)) ^ 2 + ↑(fib n) ^ 2) =
    ↑(fib (n + 1)) * (2 * ↑(fib n) + ↑(fib (n + 1)))
ring