Learning.stepsUntil_eq_dite🔗

Learning.stepsUntil_eq_dite.{u_1, u_3} {𝓐 : Type u_1} {Ω : Type u_3}
  [DecidableEq 𝓐] {A : ℕ → Ω → 𝓐} (a : 𝓐) (m : ℕ) (ω : Ω)
  [Decidable (∃ s, pullCount A a (s + 1) ω = m)] :
  stepsUntil A a m ω =
    if h : ∃ s, pullCount A a (s + 1) ω = m then ↑(Nat.find h) else ⊤
Learning.stepsUntil_eq_dite.{u_1, u_3}
  {𝓐 : Type u_1} {Ω : Type u_3}
  [DecidableEq 𝓐] {A : ℕ → Ω → 𝓐} (a : 𝓐)
  (m : ℕ) (ω : Ω)
  [Decidable
      (∃ s,
        pullCount A a (s + 1) ω = m)] :
  stepsUntil A a m ω =
    if h :
        ∃ s,
          pullCount A a (s + 1) ω = m then
      ↑(Nat.find h)
    else ⊤

lemma stepsUntil_eq_dite (a : 𝓐) (m : ℕ) (ω : Ω)
    [Decidable (∃ s, pullCount A a (s + 1) ω = m)] :
    stepsUntil A a m ω =
      if h : ∃ s, pullCount A a (s + 1) ω = m then (Nat.find h : ℕ∞) else ⊤

by
  unfold stepsUntil
  split_ifs with h'
  · refine le_antisymm ?_ ?_
    · refine sInf_le ?_
      simpa using Nat.find_spec h'
    · simp only [le_sInf_iff, Set.mem_image, Set.mem_ofPred_eq, forall_exists_index, and_imp,
        forall_apply_eq_imp_iff₂, Nat.cast_le, Nat.find_le_iff]
      exact fun n hn ↦ ⟨n, le_rfl, hn⟩
  · push Not at h'
    suffices {s | pullCount A a (s + 1) ω = m} = ∅ by simp [this]
    ext s
    simpa using (h' s)

Meaning last changed in v4.34.0-rc1-3-g2cf8f3b (2026-08-20).

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

Dependency graph

Audit surface: 2 project declarations, 32 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.