“…For example, it can be verified that any DFA that recognizes the language Sync C 4 , where C 4 is the synchronizing DFA with four states presented in Example 1.1, has at least 12 states. Among the publications in this area we should mention [72], [88], [92], [93], [119]- [121], [139], and [146]. Now we turn back to the computational complexity of synchronizability recognition.…”