unfold ulp expt
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
no_uflow : 2 ^ n ≤ a + b
carry : 2 ^ Nat.size a ≤ a + b
round_le : round (a + b) ≤ a + b
ulp_add_eq_two_mul_ulp : ulp n (a + b) = 2 * ulp n a
⊢ ulp n a ≤ 2 ^ Nat.size a
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
no_uflow : 2 ^ n ≤ a + b
carry : 2 ^ Nat.size a ≤ a + b
round_le : round (a + b) ≤ a + b
ulp_add_eq_two_mul_ulp : ulp n (a + b) = 2 * ulp n a
⊢ 2 ^ (Nat.size a - n) ≤ 2 ^ Nat.size a