Alternating finite automaton

An alternating finite automaton is like a machine that follows a set of rules to decide what to do. It is like a simple robot that can take in a sequence of symbols, like numbers or letters, and use the rules it has been programmed with to decide what to do with them. For example, it might take a sequence of letters, like A, B, C, and then it follows the rules to see what it should do with those letters. It can decide to keep going, or stop based on its rules.