rw [this]
α : Type u_1
β : Type u_2
inst✝¹ : DecidableEq α
inst✝ : DecidableEq β
s d : ℕ
hd : d ≠ 0
h : d ≤ s
x : Finset ℕ
i : ℕ
hi : i < d
this : image (fun x => i + d * x) (range ((s - i - 1) / d + 1)) = filter (fun j => j % d = i) (range s)
⊢ filter (fun j => j % d = i) (range s) = x ↔ image (fun x => i + d * x) (range ((s - i - 1) / d + 1)) = x
no goals