∀ {α : Type u_1} {β : Type u_2} [inst : Primcodable α] [inst_1 : Primcodable β] {p : α → β → Prop}
  [inst_2 : DecidableRel p],
  PrimrecRel p → ∀ {f : α → β}, Primrec f → Primrec fun a => Option.guard (fun b => decide (p a b)) (f a)