rewrite [round_eq_next_trunc_of_gt hfaithful₁ lt_round]
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
lt_round : a - b < round (a - b)
⊢ trunc n (a - b - round (a - b)) = a - b - round (a - b)
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
lt_round : a - b < round (a - b)
⊢ trunc n (a - b - next n (trunc n (a - b))) = a - b - next n (trunc n (a - b))