private Word checkConnector(int begin, int end) {
        if (end == -1) { // check connector on the left
            if (!currSen.connector.isEmpty()) {
                for (Word w : currSen.connector) {
                    int pos = WPos2Chunk(w.pos);
                    if (pos == begin || pos - 1 == begin) {
                        return w;
                    }
                }
            }
        } else {// check connector between begin and end
            for (Word w : currSen.connector) {
                int pos = WPos2Chunk(w.pos);
                if (between(begin + 1, end, pos)) {
                    return w;
                }
            }
        }
        return null;
    }