https://github.com/Michal-Witkowski/RxJava2Puzzlers
Dionysis Lorentzos, Dec 4, 2018
https://lorentzos.com/i-bet-your-rxjava-is-on-the-wrong-thread-ae02e66a3eac
Łukasz Wasylkowski, May 30, 2019
https://medium.com/@wasyl/rxjava-threading-when-subscribeon-doesnt-work-ee467a21935b
Interactive diagrams of Rx Observables