-- Mathlib/.lake/packages/lean4/src/lean/Std/Tactic/BVDecide/LRAT/Internal/Formula/RupAddSound.lean
theorem reduce_fold_fn_preserves_induction_motive {c_arr : Array (Literal (PosFin n))}
    {assignment : Array Assignment}
    (idx : Fin c_arr.size) (res : ReduceResult (PosFin n))
    (ih : ReducePostconditionInductionMotive c_arr assignment idx.1 res) :
  ReducePostconditionInductionMotive c_arr assignment (idx.1 + 1) (reduce_fold_fn assignment res c_arr[idx])

Proof state:
case inr
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
acc✝ : ReduceResult (PosFin n)
l : Literal (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) (reducedToUnit l)
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = pos
c_arr_idx_eq_false : c_arr[↑idx].snd = false
h : l = (i, b)
j_eq_idx : ↑j = ↑idx
p_entails_c_arr_j : p c_arr[↑idx].fst = false
hp : ∀ (i : PosFin n), hasAssignment (decide (p i = false)) assignment[i.val]! = false
⊢ p ⊨ (i, b)

Tactic:
specialize hp c_arr[idx.1].1

Result:
case inr
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
acc✝ : ReduceResult (PosFin n)
l : Literal (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) (reducedToUnit l)
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = pos
c_arr_idx_eq_false : c_arr[↑idx].snd = false
h : l = (i, b)
j_eq_idx : ↑j = ↑idx
p_entails_c_arr_j : p c_arr[↑idx].fst = false
hp : hasAssignment (decide (p c_arr[↑idx].fst = false)) assignment[c_arr[↑idx].fst.val]! = false
⊢ p ⊨ (i, b)

Proof state:
case inr
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
acc✝ : ReduceResult (PosFin n)
l : Literal (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) (reducedToUnit l)
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = pos
c_arr_idx_eq_false : c_arr[↑idx].snd = false
h : l = (i, b)
j_eq_idx : ↑j = ↑idx
p_entails_c_arr_j : p c_arr[↑idx].fst = false
hp : hasAssignment (decide (p c_arr[↑idx].fst = false)) assignment[c_arr[↑idx].fst.val]! = false
⊢ p ⊨ (i, b)

Tactic:
simp +decide only [p_entails_c_arr_j, decide_true, heq] at hp

Result:
no goals

Proof state:
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
hp : p ⊨ assignment
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = pos
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : reducedToUnit c_arr[↑idx] = reducedToUnit (i, b)
⊢ p ⊨ (i, b)

Tactic:
simp only [reducedToUnit.injEq] at h

Result:
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
hp : p ⊨ assignment
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = pos
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : c_arr[↑idx] = (i, b)
⊢ p ⊨ (i, b)

Proof state:
case left
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
res : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) res
h : reduce_fold_fn assignment res c_arr[↑idx] = reducedToEmpty
p : PosFin n → Bool
⊢ (∀ (i : Fin c_arr.size), ↑i < ↑idx + 1 → ¬(p ⊨ c_arr[↑i])) ∨ ¬(p ⊨ assignment)

Tactic:
rw [reduce_fold_fn.eq_def] at h

Result:
case left
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
res : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) res
h :
  (match res with
    | encounteredBoth => encounteredBoth
    | reducedToEmpty =>
      match assignment[c_arr[↑idx].fst.val]! with
      | pos => if c_arr[↑idx].snd = true then reducedToUnit c_arr[↑idx] else reducedToEmpty
      | neg => if (!c_arr[↑idx].snd) = true then reducedToUnit c_arr[↑idx] else reducedToEmpty
      | both => encounteredBoth
      | unassigned => reducedToUnit c_arr[↑idx]
    | reducedToUnit l' =>
      match assignment[c_arr[↑idx].fst.val]! with
      | pos => if c_arr[↑idx].snd = true then reducedToNonunit else reducedToUnit l'
      | neg => if (!c_arr[↑idx].snd) = true then reducedToNonunit else reducedToUnit l'
      | both => encounteredBoth
      | unassigned => reducedToNonunit
    | reducedToNonunit => reducedToNonunit) =
    reducedToEmpty
p : PosFin n → Bool
⊢ (∀ (i : Fin c_arr.size), ↑i < ↑idx + 1 → ¬(p ⊨ c_arr[↑i])) ∨ ¬(p ⊨ assignment)

Proof state:
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
hp : p ⊨ assignment
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
h : (if (!c_arr[↑idx].snd) = true then reducedToUnit c_arr[↑idx] else reducedToEmpty) = reducedToUnit (i, b)
⊢ p ⊨ (i, b)

Tactic:
split at h

Result:
case isTrue
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
hp : p ⊨ assignment
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
h✝ : (!c_arr[↑idx].snd) = true
h : reducedToUnit c_arr[↑idx] = reducedToUnit (i, b)
⊢ p ⊨ (i, b)

case isFalse
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
hp : p ⊨ assignment
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
h✝ : ¬(!c_arr[↑idx].snd) = true
h : reducedToEmpty = reducedToUnit (i, b)
⊢ p ⊨ (i, b)

Proof state:
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
h : c_arr[↑idx] = (i, b)
c_arr_idx_eq_true : b = false
hp : hasAssignment (decide (p c_arr[↑idx].fst = false)) assignment[c_arr[↑idx].fst.val]! = false
⊢ p ⊨ (i, b)

Tactic:
rw [heq] at hp

Result:
n : Nat
c_arr : Array (Literal (PosFin n))
assignment : Array Assignment
idx : Fin c_arr.size
i : PosFin n
b : Bool
p : PosFin n → Bool
j : Fin c_arr.size
j_lt_idx_add_one : ↑j < ↑idx + 1
p_entails_c_arr_j : p ⊨ c_arr[↑j]
acc✝ : ReduceResult (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) reducedToEmpty
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
h : c_arr[↑idx] = (i, b)
c_arr_idx_eq_true : b = false
hp : hasAssignment (decide (p c_arr[↑idx].fst = false)) neg = false
⊢ p ⊨ (i, b)