This question is a duplicate many times over. It might be a good idea to consolidate the questions I've linked therein. Which is the best dupe target?

D1, D2, D3.

D4, D5, D6.

D7, D8, D9.

D10, D11, D12.

D13, D14, D15.

C1, C2, C3.

C4, C5, C6.

C7, C8, C9.

C10, C11, C12.

C13, C14, C15.

Thanks, @AlexanderGruber for your recent interventions on incoming very-low-quality questions!

Consider deletion of this poor answer: math.stackexchange.com/a/3539209/9003

Close.

Sorry, my very last comment was a request to close this question. I inadvertently linked an answer.

@amWhy No problem, thanks for noticing.

@amWhy Is this the right link? I can't find your comment there.

@AlexanderGruber Oh my, I don't know how I managed to link that post!!?? Anyway, don't bother addressing that post. I appreciate your attention. Just perplexed at how I copied that link; I thought I tried to link to the mods' office!! Sorry for the confusion!

@AlexanderGruber I tend to notice these things! Thanks again!

@AlexanderGruber I think I tried to ping you about this comment of mine in the math mods' office, but may have inadvertently failed to copy, or copied a wrong link in the comment you replied to. In any case, the 10 year old user concerning me, and their post, has been dealt with.

@amWhy I see I see. I remember that flag, makes sense that'd be what that was about.