unfold go at hgo
α : Type
inst✝² : BEq α
inst✝¹ : Hashable α
inst✝ : DecidableEq α
assign : α → Bool
w : Nat
aig : AIG α
curr : Nat
hcurr : curr ≤ w
discr : aig.Ref
lhs rhs : aig.RefStream w
s : aig.RefStream curr
idx : Nat
hidx1 : idx < w
hidx2 : curr ≤ idx
res : RefStreamEntry α w
hgo : go aig curr hcurr discr lhs rhs s = res
⊢ ⟦{ aig := res.aig, ref := res.stream.getRef idx hidx1 }, assign⟧ =
    if ⟦{ aig := aig, ref := discr }, assign⟧ = true then ⟦{ aig := aig, ref := lhs.getRef idx hidx1 }, assign⟧
    else ⟦{ aig := aig, ref := rhs.getRef idx hidx1 }, assign⟧
α : Type
inst✝² : BEq α
inst✝¹ : Hashable α
inst✝ : DecidableEq α
assign : α → Bool
w : Nat
aig : AIG α
curr : Nat
hcurr : curr ≤ w
discr : aig.Ref
lhs rhs : aig.RefStream w
s : aig.RefStream curr
idx : Nat
hidx1 : idx < w
hidx2 : curr ≤ idx
res : RefStreamEntry α w
hgo :
  (if hcurr : curr < w then
      let input := { discr := discr, lhs := lhs.getRef curr hcurr, rhs := rhs.getRef curr hcurr };
      let res := aig.mkIfCached input;
      let aig_1 := res.aig;
      let ref := res.ref;
      let_fun this := ⋯;
      let discr_1 := discr.cast this;
      let lhs_1 := lhs.cast this;
      let rhs_1 := rhs.cast this;
      let s := s.cast this;
      let s := s.pushRef ref;
      go aig_1 (curr + 1) ⋯ discr_1 lhs_1 rhs_1 s
    else
      let_fun this := ⋯;
      { aig := aig, stream := this ▸ s }) =
    res
⊢ ⟦{ aig := res.aig, ref := res.stream.getRef idx hidx1 }, assign⟧ =
    if ⟦{ aig := aig, ref := discr }, assign⟧ = true then ⟦{ aig := aig, ref := lhs.getRef idx hidx1 }, assign⟧
    else ⟦{ aig := aig, ref := rhs.getRef idx hidx1 }, assign⟧