How do you depeer my customers' provider without depeering my customers? How do you cut off a router's network access without cutting off access to the networks behind it? How do you blacklist a /8 but not one of its /24s without an exemption list? How do I prevent Bob from forking my code, but allow people who fork from Bob to fork the modifications he would do to my code? How do you join tables on 2 databases when you can't authenticate to the first?