What do you mean by "it"? There is only a p2p network, with each node acting independently. Nodes which are on multiple other nodes UNLs could be considered the intersection of a set. But it makes more sense to think of it as a directed graph. There's no such think as an "untrusted validator", if you run rippled and your node isn't on anyone else's UNL, then you aren't really part of the network because your votes aren't considered in anyone else's consensus decisions (but you would get real-time access to the proposals and candidate sets).
So the set of of validators which gets used is exactly the union of nodes in the UNLs. If you have two networks without any overlap in the UNLs, then you'd get two separate ledgers.
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What do you mean by "it"? There is only a p2p network, with each node acting independently. Nodes which are on multiple other nodes UNLs could be considered the intersection of a set. But it makes more sense to think of it as a directed graph. There's no such think as an "untrusted validator", if you run rippled and your node isn't on anyone else's UNL, then you aren't really part of the network because your votes aren't considered in anyone else's consensus decisions (but you would get real-time access to the proposals and candidate sets).
So the set of of validators which gets used is exactly the union of nodes in the UNLs. If you have two networks without any overlap in the UNLs, then you'd get two separate ledgers.
http://bitcoin.stackexchange.com/questions/13330/what-is-the...
http://bitcoin.stackexchange.com/questions/10227/why-does-ri...