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Commercial agreements drive the routing policies used in today's Internet. The two most extensively studied commercial agreements are transit and peering; however, they are only two of many diverse and continuously evolving commercial agreements that ISPs enter into. So far, the only known practical safe and robust routing policy is Gao and Rexford's policy guideline, which is applicable to transit and peering agreements only. It is, therefore, of importance to identify routing policies that are safe and robust and, at the same time, capable of accommodating the diverse commercial agreements existing in the Internet. In particular, this paper investigates the extent to which routing policies can be devised to accommodate complex mutual transit agreements. We propose a series of policy guidelines that allow mutual transit agreements with progressively broader semantics to be established. Those policy guidelines guarantee routing safety and robustness as long as the autonomous system (AS) graph satisfies a corresponding set of precise topological constraints. An experimental evaluation of the proposed policy guidelines demonstrates the benefits they would likely afford in terms of routing reliability if adopted in the current Internet.