有限状态机(Finite automaton) ● Begins at go and reads the characters of its input string one at a time; If the automaton is in state g and reads input character a,it moves ("makes a transition")from state q to (q,a); Whenever its current state g is a member of A,the machine M has accepted the string read so far.An input that is not accepted is rejected. Let Ly be the set of all strings accepted by M. input (语句)：=（前缀）a state a b (前缀)=ε (前缀)：=（前缀）b(前缀)aaK前缀)ab 巴科斯范式(Backus-Naur Form,BNF) https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form• Begins at 𝑞0 and reads the characters of its input string one at a time; • If the automaton is in state 𝒒 and reads input character 𝒂, it moves (“makes a transition”) from state 𝒒 to 𝜹(𝒒, 𝒂); • Whenever its current state 𝒒 is a member of A, the machine M has accepted the string read so far. An input that is not accepted is rejected. • Let 𝐿𝑀 be the set of all strings accepted by M. 有限状态机（Finite automaton） 语句::=前缀 a 前缀::= 前缀::=前缀b | 前缀aa|前缀ab 巴科斯范式(Backus-Naur Form，BNF) https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form