@hhh Draw a triangle with vertices i, j, k with arrows i->j, j->k, k->i. Multiplying two of these units is done as follows: if they are the same, 0; if they go with the flow of the triangle, the third in the line; if the go opposite the flow, the third one as well but with a minus sign
If it's any help, I point my right thumb in the direction of the first vector, and my right forefinger in the direction of the second vector. My right middle finger can then point in the direction of the cross product.
@AsafKaragila Because he did not want to be suspended.
@hhh: When editing the OP's comments into their answer for them, you might want to mention it's the *OP*s comments, not yours, in the suggested edit description box. Generally I (and others I think) would reject an edit that put someone's personal comments into someone else's answer, so you risked getting your edit rejected. Also, I still don't see how category theory is relevant to pictorial mnemonics. :)
@hhh: You've misunderstood me; there was zero issue with what you did, in fact it was nice of you to help out the answerer and it was totally clear to those reading the answer and its comments what was going on. However, the people who review suggested edits (e.g. me) don't get to see this context, so I didn't know they were the OP's own comments until I investigated your suggested edit. I only wanted to forewarn you for your own sake that you risked getting in rejected because a reviewer...
...might not have bothered to check what was going on like I did.
@anon What is the correct terminology here to use? Look I asked the question, can I still use the term "op's comments" (not referring to myself) when I want to make answers to my questions better/clearer? Perhaps in the future, I will use the term "answerer's comments" -- is that safe?
@David : If i click on your photo icon in the chat it shows that your primary account is on StackOverflow, but it showed the other day as math.SE and even you said that you never posted anything on stackoverflow
Is there a counterexample for the claim in the question subject, that a sum of two closed sets in $\mathbb R$ is closed? If not, how can we prove it?
(By sum of sets $X+Y$ I mean the set of all sums $x+y$ where $x$ is in $X$ and $y$ is in $Y$)
Yes, I think the basic algorithm is wrong. If someone's reputation points are supposed to reflect reputation, then the votes (up or down) of former users should count just as much as the votes of current users.
Presumably then, when a person quits the site, all their questions and answers disappear. If the purpose of SE/SO is to compile a database of questions and answers, then this is the completely wrong thing to do. Imagine if somebody set fire to everything Isaac Newton ever wrote, on the day that he died. Or Thomas Jefferson. Or anyone else who's made a great contribution to the world.
@WillHunting solve the problem means solve your particular problem or it solves your problem but not fully? In the latter case, I see no issue, in the other case, I think you may have to think if you should really wait!
Some other dictionaries list that sense, too. For example, Chambers (the 11th edition) has this: "intransitive verb To make a conscious attempt to provoke controversy or disagreement on the Internet", Merriam-Webster's Advanced Learner's Dictionary says “a person who tries to cause problems on an Internet message board by posting messages that cause other people to argue, become angry, etc” for troll, Cambridge Advanced Learner's Dictionary says “to leave an insulting message on a part of the Internet for no reason”, and NOAD has "send (an e-mail message or posting on the Internet) intended…
@AsafKaragila Did you look at that call for Duplicate, I feel guilty for having to retype the same argument, I'd like if you please went through and told me if they are the duplicates of each other or not!