-- 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]! = neg
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : l = (i, b)
j_eq_idx : ↑j = ↑idx
p_entails_c_arr_j : p c_arr[↑idx].fst = true
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]! = neg
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : l = (i, b)
j_eq_idx : ↑j = ↑idx
p_entails_c_arr_j : p c_arr[↑idx].fst = true
hp : hasAssignment (decide (p c_arr[↑idx].fst = false)) assignment[c_arr[↑idx].fst.val]! = false
⊢ p ⊨ (i, b)

Proof state:
case right.h_2.h_3
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]! = both
h : encounteredBoth = reducedToUnit (i, b)
⊢ p ⊨ (i, b)

Tactic:
simp at h

Result:
no goals

Proof state:
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
⊢ (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)) ∧
    ∀ (a : PosFin n) (b : Bool),
      reduce_fold_fn assignment res c_arr[↑idx] = reducedToUnit (a, b) →
        ∀ (p : PosFin n → Bool), p ⊨ assignment → ∀ (x : Fin c_arr.size), ↑x < ↑idx + 1 → p ⊨ c_arr[↑x] → p ⊨ (a, b)

Tactic:
constructor

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
⊢ 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)

case right
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
⊢ ∀ (a : PosFin n) (b : Bool),
    reduce_fold_fn assignment res c_arr[↑idx] = reducedToUnit (a, b) →
      ∀ (p : PosFin n → Bool), p ⊨ assignment → ∀ (x : Fin c_arr.size), ↑x < ↑idx + 1 → p ⊨ c_arr[↑x] → p ⊨ (a, b)

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

Tactic:
simp at h

Result:
no goals

Proof state:
case inl
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)
l : Literal (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) (reducedToUnit l)
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : l = (i, b)
j_lt_idx : ↑j < ↑idx
⊢ p ⊨ (i, b)

Tactic:
rw [← h]

Result:
case inl
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)
l : Literal (PosFin n)
ih : ReducePostconditionInductionMotive c_arr assignment (↑idx) (reducedToUnit l)
x✝ : Assignment
heq : assignment[c_arr[↑idx].fst.val]! = neg
c_arr_idx_eq_true : c_arr[↑idx].snd = true
h : l = (i, b)
j_lt_idx : ↑j < ↑idx
⊢ p ⊨ l