 Therefore mule is a relevant alternative to not-mule. Furthermore, you fail to know not-mule since you cannot rule out mule: you believe not-mule on the basis of your zebra-in-the-cage percepts, but you would still have these if mule held, contrary to CRR. Yet you know zeb in spite of your inability to rule out mule, for were zeb false you would not have your zebra-in-the-cage percepts.