http://tau-cm.wikidot.com/forum/t-250795/2007 ]]>

The answer is listed as P, but how can that be? We are either running the DFA and the NFA, which means we're running non-deterministically on one of them (or on the cartesian multiplication that is the intersection which is still non-deterministic), or we are running on the DFA version of the NFA which needs to be created and is potentially exponential.

How can we run NFAs on a non-deterministic machine (as to be in P) and not use the same exponential algorithm we use to simulate the non-deterministic TM?

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