and we might have a small number of labeled audio to sentence and files and a ton of audio data that haven't been labeled so basically this is used in any task that requires a big amount of human resources to do the labeling and when there's a big amount of possibilities so the characteristics here are that we have a huge amount of unlabeled data otherwise we would just use a supervised learning algorithm and there's an input/output proximity symmetry so what does that mean it basically means that the underlying requirement here is that