. simp only [Prod.exists, Bool.exists_bool, not_exists, not_or, unit] at hl
  split
  . next some_eq_none =>
    simp only at some_eq_none
  . next l _ _ heq =>
    simp only [Option.some.injEq] at heq
    rw [heq] at hl
    specialize hl l.1
    simp only [DefaultClause.mk.injEq, List.cons.injEq, and_true] at hl
    by_cases hl2 : l.2
    . simp only [← hl2, Prod.mk.eta, not_true, and_false] at hl
    . simp only [Bool.not_eq_true] at hl2
      simp only [← hl2, Prod.mk.eta, not_true, false_and] at hl
  . have deleteOne_f_rw : deleteOne f id = ⟨Array.set! f.clauses id none, f.rupUnits, f.ratUnits, f.assignments⟩ := by
      simp only [deleteOne]
      split
      . next heq2 =>
        simp only [heq] at heq2
      . next l _ _ heq2 =>
        simp only [heq, Option.some.injEq] at heq2
        rw [heq2] at hl
        specialize hl l.1
        simp only [DefaultClause.mk.injEq, List.cons.injEq, and_true] at hl
        by_cases hl2 : l.2
        . simp only [← hl2, Prod.mk.eta, not_true, and_false] at hl
        . simp only [Bool.not_eq_true] at hl2
          simp only [← hl2, Prod.mk.eta, not_true, false_and] at hl
      . rfl
    simp only [deleteOne_f_rw] at hb
    specialize hf i b hb
    simp only [toList, Array.toList_eq, List.append_assoc, List.mem_append, List.mem_filterMap, id_eq,
      exists_eq_right, List.mem_map, Prod.exists, Bool.exists_bool] at hf
    simp only [toList, Array.toList_eq, List.append_assoc, List.mem_append, List.mem_filterMap, id_eq,
      exists_eq_right, List.mem_map, Prod.exists, Bool.exists_bool]
    rcases hf with hf | hf
    . apply Or.inl
      simp only [Array.set!, Array.setD]
      split
      . rcases List.get_of_mem hf with ⟨idx, hidx⟩
        simp only [← hidx, Array.data_set]
        rw [List.mem_iff_get]
        have idx_in_bounds : idx.1 < List.length (List.set f.clauses.data id none) := by
          simp only [List.length_set]
          exact idx.2
        apply Exists.intro ⟨idx.1, idx_in_bounds⟩
        by_cases id = idx
        . next id_eq_idx =>
          exfalso
          have idx_in_bounds2 : idx.1 < f.clauses.size := by
            have f_clauses_rw : f.clauses = { data := f.clauses.data } := rfl
            conv => rhs; rw [f_clauses_rw, Array.size_mk]
            exact idx.2
          simp only [getElem!, id_eq_idx, Array.data_length, idx_in_bounds2, ↓reduceDite,
            Fin.eta, Array.get_eq_getElem, Array.getElem_eq_data_get] at heq
          rw [hidx] at heq
          simp only [Option.some.injEq] at heq
          rw [← heq] at hl
          specialize hl i
          simp only [unit, DefaultClause.mk.injEq, List.cons.injEq, Prod.mk.injEq, true_and, and_true,
            Bool.not_eq_false, Bool.not_eq_true] at hl
          by_cases b_val : b
          . simp only [b_val, and_false] at hl
          . simp only [b_val, false_and] at hl
        . next id_ne_idx =>
          simp only [ne_eq, id_ne_idx, not_false_eq_true, List.get_set_ne]
      . exact hf
    . exact Or.inr hf
case neg
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hf : ∀ (i : PosFin n) (b : Bool), hasAssignment b f.assignments[i.val] = true → unit (i, b) ∈ f.toList
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
hb : hasAssignment b (f.deleteOne id).assignments[i.val] = true
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
hl : ¬∃ l, c = unit l
⊢ unit (i, b) ∈
    (match some c with
      | none => { clauses := f.clauses, rupUnits := f.rupUnits, ratUnits := f.ratUnits, assignments := f.assignments }
      | some { clause := [l], nodupkey := nodupkey, nodup := nodup } =>
        { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
          assignments := f.assignments.modify l.fst.val (removeAssignment l.snd) }
      | some val =>
        { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits,
          assignments := f.assignments }).toList
no goals