type storage is unit
type return is list (operation) * storage

function cb (const s : storage) : return is
  block {
    const c : contract(unit) = get_contract(sender)
  }
  with (list [transaction(unit, 0mutez, c)], s)


function cbo (const s : unit) : return is
  block {
    const c : contract (unit) =
      case (get_contract_opt(sender) : option(contract(unit))) of
        Some (c) -> c
      | None -> (failwith ("contract not found") : contract (unit))
      end
  }
  with (list [transaction(unit, 0mutez, c)], s)