sum_mod_range🔗

sum_mod_range {K : ℕ} (hK : 0 < K) (a : Fin K) :
  (∑ s ∈ Finset.range K, if ⟨s % K, ⋯⟩ = a then 1 else 0) = 1
sum_mod_range {K : ℕ} (hK : 0 < K)
  (a : Fin K) :
  (∑ s ∈ Finset.range K,
      if ⟨s % K, ⋯⟩ = a then 1 else 0) =
    1

lemma sum_mod_range {K : ℕ} (hK : 0 < K) (a : Fin K) :
    (∑ s ∈ range K, if ⟨s % K, Nat.mod_lt _ hK⟩ = a then 1 else 0) = 1

by
  have h_iff (s : ℕ) (hs : s < K) : ⟨s % K, Nat.mod_lt _ hK⟩ = a ↔ s = a := by
    simp only [Nat.mod_eq_of_lt hs, Fin.ext_iff]
  calc (∑ s ∈ range K, if ⟨s % K, Nat.mod_lt _ hK⟩ = a then 1 else 0)
  _ = ∑ s ∈ range K, if s = a then 1 else 0 := sum_congr rfl fun s hs ↦ by grind
  _ = _ := by
    rw [sum_ite_eq']
    simp

Meaning unchanged since v4.33.0-rc1-29-gce231eb, the oldest revision on record (2026-07-30).

Self-contained, with its dependencies inlined and proofs replaced by sorry: download the raw file · open it in the Lean web editor.

Dependency graph

Nothing to draw. Its statement rests on no other declaration in this project, and names nothing from a package left unaudited — so the graph is this declaration alone. That is the answer, not a missing picture.

Audit surface: 0 project declarations, 17 external constants

✓ Proved: no sorry anywhere in its closure

This is the tool's own reading of one build's recorded axioms, and it is not robust against an author who wants it to pass. Checking meant to be relied on should go through Comparator, which replays the proof through the kernel from an export against an explicit list of permitted axioms.