p : ℕ → Prop
inst✝ : DecidablePred p
a b : ℕ
⊢ count (fun k => p (b + k)) a + count p b = count (fun k => p (k + b)) a + count p b
p : ℕ → Prop
inst✝ : DecidablePred p
a b : ℕ
⊢ count p (a + b) = count (fun k => p (k + b)) a + count p b
rw [add_comm, count_add, add_comm]
no goals
p : ℕ → Prop
inst✝ : DecidablePred p
a b : ℕ
⊢ count (fun k => p (b + k)) a + count p b = count (fun k => p (k + b)) a + count p b
simp_rw [add_comm b]