Regular expressions, at least using the computer science definition, are equivalent in expressive power to the regular langauges, hence their name. This means they can be defined in terms of a deterministic or non-deterministic finite automata. Adding a stack would give us a push-down automata, which can recognize context-free languages. Adding a second stack gives us something equivalent in power to a Turing machine.

In reply to Re^2: Negating Regexes: Tips, Tools, And Tricks Of The Trade by geekphilosopher
in thread Negating Regexes: Tips, Tools, And Tricks Of The Trade by Limbic~Region

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