start state: if input == 1 then fail start state: if input == 2 then fail start state: if input == 3 then fail ... ! state 2: if input == 0 then goto state 3 state 2: if input == 1 then fail state 2: if input == 2 then fail state 2: if input == 3 then fail ... ! state 3: for any input, accept REGULAR