@user21820 Regarding D1, I agree that it is not a good question. However, I would like to solicit opinions about how such puzzles can be presented on MSE (rather than
Puzzling) without being off-topic. IMO, adding an attempt does
not improve such a question, and I am not sure that a link to a source is necessarily sufficient. Is it possible for such a question to be really on-topic here (again, rather than on
Puzzling)?