Tighter Construction of Tight Büchi Automata

Tight automata are useful in providing the shortest counterexample in LTL model checking and also in constructing a maximally satisfying strategy in LTL strategy synthesis. There exists a translation of LTL formulas to tight Büchi automata and several translations of Büchi automata to equivalent tight Büchi automata. This paper presents another translation of Büchi automata to equivalent tight Büchi automata. The translation is designed to produce smaller tight automata and it asymptotically improves the best-known upper bound on the size of a tight Büchi automaton equivalent to a given Büchi automaton. We also provide a lower bound, which is more precise than the previously known one. Further, we show that automata reduction methods based on quotienting preserve tightness. Our translation was implemented in a tool called Tightener. Experimental evaluation shows that Tightener usually produces smaller tight automata than the translation from LTL to tight automata known as CGH.