. have rupHint_clause_options :
    f.clauses[rupHints[i.1]]? = none ∨ f.clauses[rupHints[i.1]]? = some none ∨ ∃ c, f.clauses[rupHints[i.val]]? = some (some c) := by
    match f.clauses[rupHints[i.val]]? with
    | none => exact Or.inl rfl
    | some none => exact Or.inr $ Or.inl rfl
    | some (some c) => exact (Or.inr ∘ Or.inr ∘ Exists.intro c) rfl
  rcases rupHint_clause_options with rupHint_clause_eq_none | rupHint_clause_eq_some_none | ⟨c, rupHint_clause_eq_c⟩
  . simp only [rupHint_clause_eq_none]
    exact ih
  . simp only [rupHint_clause_eq_some_none]
    exact ih
  . simp only [rupHint_clause_eq_c]
    have reduce_c_options : reduce c acc.1 = ReduceResult.encounteredBoth ∨ reduce c acc.1 = ReduceResult.reducedToEmpty ∨
      (∃ l : Literal (PosFin n), reduce c acc.1 = ReduceResult.reducedToUnit l) ∨ reduce c acc.1 = ReduceResult.reducedToNonunit := by
      match reduce c acc.fst with
      | ReduceResult.encounteredBoth => exact Or.inl rfl
      | ReduceResult.reducedToEmpty => exact (Or.inr ∘ Or.inl) rfl
      | ReduceResult.reducedToUnit l => exact (Or.inr ∘ Or.inr ∘ Or.inl ∘ Exists.intro l) rfl
      | ReduceResult.reducedToNonunit => exact (Or.inr ∘ Or.inr ∘ Or.inr) rfl
    rcases reduce_c_options with hencounteredBoth | hreducedToEmpty | ⟨l, hreducedToUnit⟩ | hreducedToNonunit
    . simp only [hencounteredBoth]
      exact ih
    . simp only [hreducedToEmpty]
      exact ih
    . simp only [hreducedToUnit, Prod.mk.eta]
      by_cases h : hasAssignment l.snd acc.fst[l.fst.val]!
      . simp only [h, ite_true]
        exact ih
      . simp only [h, ite_false]
        exact confirmRupHint_preserves_invariant_helper f f_assignments_size acc hsize l ih h
    . simp only [hreducedToNonunit]
      exact ih
case intro.isFalse
n : Nat
f : DefaultFormula n
f_assignments_size : f.assignments.size = n
rupHints : Array Nat
i : Fin rupHints.size
acc : Array Assignment × List (Literal (PosFin n)) × Bool × Bool
hsize : acc.fst.size = n
ih : f.derivedLits_invariant f_assignments_size acc.fst hsize acc.snd.fst
hsize' : (confirmRupHint f.clauses acc rupHints[i]).fst.size = n
h✝ : ¬(acc.2.2.snd || acc.2.2.fst) = true
⊢ f.derivedLits_invariant f_assignments_size
    (match f.clauses[rupHints[↑i]]? with
      | some (some c) =>
        match c.reduce acc.fst with
        | ReduceResult.encounteredBoth => (acc.fst, acc.2.fst, true, false)
        | ReduceResult.reducedToEmpty => (acc.fst, acc.2.fst, true, false)
        | ReduceResult.reducedToUnit (l, b) =>
          if hasAssignment b acc.fst[l.val]! = true then (acc.fst, acc.2.fst, false, false)
          else (acc.fst.modify l.val (addAssignment b), (l, b) :: acc.2.fst, false, false)
        | ReduceResult.reducedToNonunit => (acc.fst, acc.2.fst, false, true)
      | some none => (acc.fst, acc.2.fst, false, true)
      | none => (acc.fst, acc.2.fst, false, true)).fst
    ⋯
    (match f.clauses[rupHints[↑i]]? with
        | some (some c) =>
          match c.reduce acc.fst with
          | ReduceResult.encounteredBoth => (acc.fst, acc.2.fst, true, false)
          | ReduceResult.reducedToEmpty => (acc.fst, acc.2.fst, true, false)
          | ReduceResult.reducedToUnit (l, b) =>
            if hasAssignment b acc.fst[l.val]! = true then (acc.fst, acc.2.fst, false, false)
            else (acc.fst.modify l.val (addAssignment b), (l, b) :: acc.2.fst, false, false)
          | ReduceResult.reducedToNonunit => (acc.fst, acc.2.fst, false, true)
        | some none => (acc.fst, acc.2.fst, false, true)
        | none => (acc.fst, acc.2.fst, false, true)).snd.fst
no goals