abstract:In automata theory, a nondeterministic finite automaton (NFA), or nondeterministic finite state machine, is a finite state machine that (1) does not require input symbols for state transitions and (2) is capable of transitioning to zero or two or more states for a given start state and input symbol. This distinguishes it from a deterministic finite automaton (DFA), in which all transitions are uniquely determined and in which an input symbol is required for all state transitions.