. 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
case pos
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
hl :
  ∀ (x : PosFin n),
    ¬c = { clause := [(x, false)], nodupkey := ⋯, nodup := ⋯ } ∧
      ¬c = { clause := [(x, true)], nodupkey := ⋯, nodup := ⋯ }
x✝¹ : Option (DefaultClause n)
val✝ : DefaultClause n
x✝ :
  ∀ (l : Literal (PosFin n)) (nodupkey : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l])
    (nodup : [l].Nodup), val✝ = { clause := [l], nodupkey := nodupkey, nodup := nodup } → False
heq✝ : some c = some val✝
deleteOne_f_rw :
  f.deleteOne id =
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits, assignments := f.assignments }
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.data
h✝¹ : id < f.clauses.size
idx : Fin f.clauses.data.length
hidx : f.clauses.data.get idx = some (unit (i, b))
idx_in_bounds : ↑idx < (f.clauses.data.set id none).length
h✝ : id = ↑idx
⊢ (f.clauses.data.set id none).get ⟨↑idx, idx_in_bounds⟩ = f.clauses.data.get idx

case neg
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
hl :
  ∀ (x : PosFin n),
    ¬c = { clause := [(x, false)], nodupkey := ⋯, nodup := ⋯ } ∧
      ¬c = { clause := [(x, true)], nodupkey := ⋯, nodup := ⋯ }
x✝¹ : Option (DefaultClause n)
val✝ : DefaultClause n
x✝ :
  ∀ (l : Literal (PosFin n)) (nodupkey : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l])
    (nodup : [l].Nodup), val✝ = { clause := [l], nodupkey := nodupkey, nodup := nodup } → False
heq✝ : some c = some val✝
deleteOne_f_rw :
  f.deleteOne id =
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits, assignments := f.assignments }
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.data
h✝¹ : id < f.clauses.size
idx : Fin f.clauses.data.length
hidx : f.clauses.data.get idx = some (unit (i, b))
idx_in_bounds : ↑idx < (f.clauses.data.set id none).length
h✝ : ¬id = ↑idx
⊢ (f.clauses.data.set id none).get ⟨↑idx, idx_in_bounds⟩ = f.clauses.data.get idx
case neg
n : Nat
f : DefaultFormula n
id : Nat
hsize : f.assignments.size = n
hsize' : (f.deleteOne id).assignments.size = n
i : PosFin n
b : Bool
i_in_bounds : i.val < f.assignments.size
c : DefaultClause n
heq : f.clauses[id]! = some c
hl :
  ∀ (x : PosFin n),
    ¬c = { clause := [(x, false)], nodupkey := ⋯, nodup := ⋯ } ∧
      ¬c = { clause := [(x, true)], nodupkey := ⋯, nodup := ⋯ }
x✝¹ : Option (DefaultClause n)
val✝ : DefaultClause n
x✝ :
  ∀ (l : Literal (PosFin n)) (nodupkey : ∀ (l_1 : PosFin n), ¬(l_1, true) ∈ [l] ∨ ¬(l_1, false) ∈ [l])
    (nodup : [l].Nodup), val✝ = { clause := [l], nodupkey := nodupkey, nodup := nodup } → False
heq✝ : some c = some val✝
deleteOne_f_rw :
  f.deleteOne id =
    { clauses := f.clauses.set! id none, rupUnits := f.rupUnits, ratUnits := f.ratUnits, assignments := f.assignments }
hb : hasAssignment b f.assignments[i.val] = true
hf : some (unit (i, b)) ∈ f.clauses.data
h✝¹ : id < f.clauses.size
idx : Fin f.clauses.data.length
hidx : f.clauses.data.get idx = some (unit (i, b))
idx_in_bounds : ↑idx < (f.clauses.data.set id none).length
h✝ : ¬id = ↑idx
⊢ (f.clauses.data.set id none).get ⟨↑idx, idx_in_bounds⟩ = f.clauses.data.get idx