graceful exit
graceful degradation
fail-safe
https://source.unsplash.com/featured/?graceful-exit#.png
/suto3/google.icongraceful exit
/suto3/Google画像検索.icongraceful exit
/suto3/Google定義検索.icon graceful exit
/suto3/wikipedia.icongraceful exit
/suto3/weblio.icon graceful exit
/suto3/kotobank.icon graceful exit
/suto3/jisho.icon graceful exit