-- Mathlib/.lake/packages/lean4/src/lean/Std/Tactic/BVDecide/LRAT/Internal/Formula/RatAddResult.lean
theorem clear_insertRat {n : Nat} (f : DefaultFormula n)
    (hf : f.ratUnits = #[] ∧ f.assignments.size = n) (units : CNF.Clause (PosFin n)) :
    clearRatUnits (f.insertRatUnits units).1 = f

Proof state:
case assignments.intro
n : Nat
f : DefaultFormula n
hf : f.ratUnits = #[] ∧ f.assignments.size = n
units : CNF.Clause (PosFin n)
motive : Nat → Array Assignment → Prop := f.ClearInsertInductionMotive ⋯ (f.insertRatUnits units).fst.ratUnits
h_base : motive 0 (f.insertRatUnits units).fst.assignments
h_inductive :
  ∀ (idx : Fin (f.insertRatUnits units).fst.ratUnits.size) (assignments : Array Assignment),
    motive (↑idx) assignments → motive (↑idx + 1) (clearUnit assignments (f.insertRatUnits units).fst.ratUnits[idx])
h_size : (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits).size = n
h :
  ∀ (i : Fin n),
    let_fun i_lt_assignments_size := ⋯;
    let_fun i_lt_f_assignments_size := ⋯;
    let assignments_i :=
      (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits)[↑i];
    let fassignments_i := f.assignments[↑i];
    (assignments_i = fassignments_i ∧
        ∀ (j : Fin (f.insertRatUnits units).fst.ratUnits.size),
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size → (f.insertRatUnits units).fst.ratUnits[j].fst.val ≠ ↑i) ∨
      (∃ j b i_gt_zero,
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            (f.insertRatUnits units).fst.ratUnits[j] = (⟨↑i, ⋯⟩, b) ∧
              assignments_i = addAssignment b fassignments_i ∧
                ¬hasAssignment b fassignments_i = true ∧
                  ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                    ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                      k ≠ j → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i) ∨
        ∃ j1 j2 i_gt_zero,
          ↑j1 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            ↑j2 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
              (f.insertRatUnits units).fst.ratUnits[j1] = (⟨↑i, ⋯⟩, true) ∧
                (f.insertRatUnits units).fst.ratUnits[j2] = (⟨↑i, ⋯⟩, false) ∧
                  assignments_i = both ∧
                    fassignments_i = unassigned ∧
                      ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                        ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                          k ≠ j1 → k ≠ j2 → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i
⊢ Array.foldl clearUnit (f.insertRatUnits units).1.assignments (f.insertRatUnits units).1.ratUnits = f.assignments

Tactic:
apply Array.ext

Result:
case assignments.intro.h₁
n : Nat
f : DefaultFormula n
hf : f.ratUnits = #[] ∧ f.assignments.size = n
units : CNF.Clause (PosFin n)
motive : Nat → Array Assignment → Prop := f.ClearInsertInductionMotive ⋯ (f.insertRatUnits units).fst.ratUnits
h_base : motive 0 (f.insertRatUnits units).fst.assignments
h_inductive :
  ∀ (idx : Fin (f.insertRatUnits units).fst.ratUnits.size) (assignments : Array Assignment),
    motive (↑idx) assignments → motive (↑idx + 1) (clearUnit assignments (f.insertRatUnits units).fst.ratUnits[idx])
h_size : (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits).size = n
h :
  ∀ (i : Fin n),
    let_fun i_lt_assignments_size := ⋯;
    let_fun i_lt_f_assignments_size := ⋯;
    let assignments_i :=
      (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits)[↑i];
    let fassignments_i := f.assignments[↑i];
    (assignments_i = fassignments_i ∧
        ∀ (j : Fin (f.insertRatUnits units).fst.ratUnits.size),
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size → (f.insertRatUnits units).fst.ratUnits[j].fst.val ≠ ↑i) ∨
      (∃ j b i_gt_zero,
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            (f.insertRatUnits units).fst.ratUnits[j] = (⟨↑i, ⋯⟩, b) ∧
              assignments_i = addAssignment b fassignments_i ∧
                ¬hasAssignment b fassignments_i = true ∧
                  ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                    ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                      k ≠ j → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i) ∨
        ∃ j1 j2 i_gt_zero,
          ↑j1 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            ↑j2 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
              (f.insertRatUnits units).fst.ratUnits[j1] = (⟨↑i, ⋯⟩, true) ∧
                (f.insertRatUnits units).fst.ratUnits[j2] = (⟨↑i, ⋯⟩, false) ∧
                  assignments_i = both ∧
                    fassignments_i = unassigned ∧
                      ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                        ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                          k ≠ j1 → k ≠ j2 → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i
⊢ (Array.foldl clearUnit (f.insertRatUnits units).1.assignments (f.insertRatUnits units).1.ratUnits).size =
    f.assignments.size

case assignments.intro.h₂
n : Nat
f : DefaultFormula n
hf : f.ratUnits = #[] ∧ f.assignments.size = n
units : CNF.Clause (PosFin n)
motive : Nat → Array Assignment → Prop := f.ClearInsertInductionMotive ⋯ (f.insertRatUnits units).fst.ratUnits
h_base : motive 0 (f.insertRatUnits units).fst.assignments
h_inductive :
  ∀ (idx : Fin (f.insertRatUnits units).fst.ratUnits.size) (assignments : Array Assignment),
    motive (↑idx) assignments → motive (↑idx + 1) (clearUnit assignments (f.insertRatUnits units).fst.ratUnits[idx])
h_size : (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits).size = n
h :
  ∀ (i : Fin n),
    let_fun i_lt_assignments_size := ⋯;
    let_fun i_lt_f_assignments_size := ⋯;
    let assignments_i :=
      (Array.foldl clearUnit (f.insertRatUnits units).fst.assignments (f.insertRatUnits units).fst.ratUnits)[↑i];
    let fassignments_i := f.assignments[↑i];
    (assignments_i = fassignments_i ∧
        ∀ (j : Fin (f.insertRatUnits units).fst.ratUnits.size),
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size → (f.insertRatUnits units).fst.ratUnits[j].fst.val ≠ ↑i) ∨
      (∃ j b i_gt_zero,
          ↑j ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            (f.insertRatUnits units).fst.ratUnits[j] = (⟨↑i, ⋯⟩, b) ∧
              assignments_i = addAssignment b fassignments_i ∧
                ¬hasAssignment b fassignments_i = true ∧
                  ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                    ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                      k ≠ j → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i) ∨
        ∃ j1 j2 i_gt_zero,
          ↑j1 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
            ↑j2 ≥ (f.insertRatUnits units).fst.ratUnits.size ∧
              (f.insertRatUnits units).fst.ratUnits[j1] = (⟨↑i, ⋯⟩, true) ∧
                (f.insertRatUnits units).fst.ratUnits[j2] = (⟨↑i, ⋯⟩, false) ∧
                  assignments_i = both ∧
                    fassignments_i = unassigned ∧
                      ∀ (k : Fin (f.insertRatUnits units).fst.ratUnits.size),
                        ↑k ≥ (f.insertRatUnits units).fst.ratUnits.size →
                          k ≠ j1 → k ≠ j2 → (f.insertRatUnits units).fst.ratUnits[k].fst.val ≠ ↑i
⊢ ∀ (i : Nat)
    (hi₁ : i < (Array.foldl clearUnit (f.insertRatUnits units).1.assignments (f.insertRatUnits units).1.ratUnits).size)
    (hi₂ : i < f.assignments.size),
    (Array.foldl clearUnit (f.insertRatUnits units).1.assignments (f.insertRatUnits units).1.ratUnits)[i] =
      f.assignments[i]