public boolean tryDelta(byte symbol) {
            int lastHash=hash;
            int lastState=state;
            delta(symbol);
            if (isValid()) return true;

            hash=lastHash;
            state=lastState;
            return false;
        }
Returns whether the given symbol would take us to a valid state, without changing the state
fsa/src/main/java/com/yahoo/fsa/FSA.java