A Buchi automaton is a regular automaton but reads infinite words instead of finite words. A word is defined to be in the language of the automaton iff a run of the automaton on it visits inifinitly...
A co-buchi automaton is defined similarly to a buchi one: A = <Q,\Sigma, Q0, \delta, F>.
The acceptance condition of a co-Buchi automaton is: for an infinite word w, w is in L(A) (A's...