rewrite [round_eq, tsub_self, trunc_zero]
round : ℕ → ℕ
n a b : ℕ
round_eq : round (a - b) = a - b
⊢ trunc n (a - b - round (a - b)) = a - b - round (a - b) ∧ trunc n (round (a - b) - (a - b)) = round (a - b) - (a - b)
round : ℕ → ℕ
n a b : ℕ
round_eq : round (a - b) = a - b
⊢ 0 = 0 ∧ 0 = 0