005 Subscription-Object
https://rxjs.dev/guide/subscription

006 RxJS-Reference
https://rxjs.dev/api

009 JSON-Placeholder
https://jsonplaceholder.typicode.com/

012 Map-Operator
https://rxjs.dev/api/operators/map

017 JSON-Placeholder-URL
https://jsonplaceholder.typicode.com/todos/1