I don't have the rep to close questions or shut people down, but perhaps one day I will have.
Mari-Lou, bless her, just told me not to feed a troll. Now, I have encountered some of the wickedest trolls on the net, I know from trolls. And I don't think this one is a troll, just stupid. I see no malice there. Likewise with another questioner who keeps getting told the same thing and not believing it. I itch to ask him – if he, a Frenchman, knows English better than us, why is he here?
We try to be nice, but some people make it very difficult. "Against stupidity the gods themselves struggle in vain", wrote Schiller.
Is there a standard for how many times you should tell a person the same thing before giving up on him?