. next hlt =>
  cases Nat.eq_or_lt_of_le hidx2 with
  | inl heq =>
    rw [← hgo]
    rw [go_getRef (hidx := by omega)]
    rw [AIG.RefStream.getRef_push_ref_eq' (hidx := by rw [heq])]
    simp only [← heq]
    rw [go_denote_mem_prefix]
    . unfold mkFullAdder
      simp [hcin]
    . simp only [Ref_cast']
      apply Ref.hgate
  | inr hlt =>
    rw [← hgo]
    rw [go_eq_eval_getLsb (lhsExpr := lhsExpr) (rhsExpr := rhsExpr) (curr := curr + 1)]
    . rw [mkFullAdder_denote_mem_prefix]
      rw [mkFullAdder_denote_mem_prefix]
      . simp
      . simp [Ref.hgate]
      . simp [Ref.hgate]
    . intro idx hidx
      rw [mkFullAdder_denote_mem_prefix]
      rw [← hleft idx hidx]
      . simp
      . simp [Ref.hgate]
    . intro idx hidx
      rw [mkFullAdder_denote_mem_prefix]
      rw [← hright idx hidx]
      . simp
      . simp [Ref.hgate]
    . unfold mkFullAdder
      simp only [Ref_cast', id_eq, Int.reduceNeg, denote_projected_entry, denote_mkFullAdderCarry,
        FullAdderInput.lhs_cast, FullAdderInput.rhs_cast, FullAdderInput.cin_cast,
        BitVec.carry_succ]
      rw [AIG.LawfulOperator.denote_mem_prefix (f := mkFullAdderOut)]
      rw [AIG.LawfulOperator.denote_mem_prefix (f := mkFullAdderOut)]
      rw [AIG.LawfulOperator.denote_mem_prefix (f := mkFullAdderOut)]
      rw [hleft, hright, hcin]
      simp [_root_.Bool.atLeastTwo_eq_halfAdder]
    . omega
case isTrue
α : Type
inst✝² : BEq α
inst✝¹ : Hashable α
inst✝ : DecidableEq α
w : Nat
aig : AIG α
curr : Nat
hcurr : curr ≤ w
cin : aig.Ref
s : aig.RefStream curr
lhs rhs : aig.RefStream w
assign : α → Bool
lhsExpr rhsExpr : BitVec w
hleft : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := lhs.getRef idx hidx }, assign⟧ = lhsExpr.getLsb idx
hright : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := rhs.getRef idx hidx }, assign⟧ = rhsExpr.getLsb idx
hcin : ⟦{ aig := aig, ref := cin }, assign⟧ = BitVec.carry curr lhsExpr rhsExpr false
idx : Nat
hidx1 : idx < w
hidx2 : curr ≤ idx
res : RefStreamEntry α w
h✝ : curr < w
hgo :
  go (mkFullAdder aig { lhs := lhs.getRef curr h✝, rhs := rhs.getRef curr h✝, cin := cin }).aig (curr + 1) ⋯
      (mkFullAdder aig { lhs := lhs.getRef curr h✝, rhs := rhs.getRef curr h✝, cin := cin }).cout
      ((s.cast ⋯).pushRef (mkFullAdder aig { lhs := lhs.getRef curr h✝, rhs := rhs.getRef curr h✝, cin := cin }).out)
      (lhs.cast ⋯) (rhs.cast ⋯) =
    res
⊢ ⟦{ aig := res.aig, ref := res.stream.getRef idx hidx1 }, assign⟧ =
    ⟦{ aig := aig, ref := lhs.getRef idx hidx1 }, assign⟧.xor
      (⟦{ aig := aig, ref := rhs.getRef idx hidx1 }, assign⟧.xor (BitVec.carry idx lhsExpr rhsExpr false))

case isFalse
α : Type
inst✝² : BEq α
inst✝¹ : Hashable α
inst✝ : DecidableEq α
w : Nat
aig : AIG α
curr : Nat
hcurr : curr ≤ w
cin : aig.Ref
s : aig.RefStream curr
lhs rhs : aig.RefStream w
assign : α → Bool
lhsExpr rhsExpr : BitVec w
hleft : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := lhs.getRef idx hidx }, assign⟧ = lhsExpr.getLsb idx
hright : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := rhs.getRef idx hidx }, assign⟧ = rhsExpr.getLsb idx
hcin : ⟦{ aig := aig, ref := cin }, assign⟧ = BitVec.carry curr lhsExpr rhsExpr false
idx : Nat
hidx1 : idx < w
hidx2 : curr ≤ idx
res : RefStreamEntry α w
h✝ : ¬curr < w
hgo : { aig := aig, stream := ⋯ ▸ s } = res
⊢ ⟦{ aig := res.aig, ref := res.stream.getRef idx hidx1 }, assign⟧ =
    ⟦{ aig := aig, ref := lhs.getRef idx hidx1 }, assign⟧.xor
      (⟦{ aig := aig, ref := rhs.getRef idx hidx1 }, assign⟧.xor (BitVec.carry idx lhsExpr rhsExpr false))
case isFalse
α : Type
inst✝² : BEq α
inst✝¹ : Hashable α
inst✝ : DecidableEq α
w : Nat
aig : AIG α
curr : Nat
hcurr : curr ≤ w
cin : aig.Ref
s : aig.RefStream curr
lhs rhs : aig.RefStream w
assign : α → Bool
lhsExpr rhsExpr : BitVec w
hleft : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := lhs.getRef idx hidx }, assign⟧ = lhsExpr.getLsb idx
hright : ∀ (idx : Nat) (hidx : idx < w), ⟦{ aig := aig, ref := rhs.getRef idx hidx }, assign⟧ = rhsExpr.getLsb idx
hcin : ⟦{ aig := aig, ref := cin }, assign⟧ = BitVec.carry curr lhsExpr rhsExpr false
idx : Nat
hidx1 : idx < w
hidx2 : curr ≤ idx
res : RefStreamEntry α w
h✝ : ¬curr < w
hgo : { aig := aig, stream := ⋯ ▸ s } = res
⊢ ⟦{ aig := res.aig, ref := res.stream.getRef idx hidx1 }, assign⟧ =
    ⟦{ aig := aig, ref := lhs.getRef idx hidx1 }, assign⟧.xor
      (⟦{ aig := aig, ref := rhs.getRef idx hidx1 }, assign⟧.xor (BitVec.carry idx lhsExpr rhsExpr false))