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If you `launch(EmptyCoroutineContext)` or `launch(Unconfined)` in UI thread, then after the first async operation like `delay` you’ll resume in some other thread and will not be in UI thread anymore. However, with `launch(UI)` you always resume in UI thread, guaranteed. It is explained with examples in this section of the guide: <https://github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md#unconfined-vs-confined-dispatcher>