rw[ih]
case fst
a✝ α✝ β✝ : Ty
p : Exp (Ty.prod α✝ β✝)
ih : denote p = denote (cfold p)
⊢ (denote p).fst =
    denote
      (match pairOut (cfold p) with
      | some p => p.fst
      | none => fst (cfold p))
case fst
a✝ α✝ β✝ : Ty
p : Exp (Ty.prod α✝ β✝)
ih : denote p = denote (cfold p)
⊢ (denote (cfold p)).fst =
    denote
      (match pairOut (cfold p) with
      | some p => p.fst
      | none => fst (cfold p))