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> You could always use a calculator but the whole 'show your own working' catch meant you had to do it all manually. Not any more!

You could often cheat (for equation rearrangement questions) if you knew the answer by simply working backwards towards the question, this is often easier than going from problem to solution but still provides all of the steps along the way.

I remember one maths teacher hinting at this trick, especially to understand the derivation of the quadratic formula:-

    ax^2 + bx + c = 0
by starting with:-

    x = ( -b +/- sqrt( b^2 - 4ac ) ) / 2a
and working backwards.


There is also "solving by assuming the negative". It's a technique for problems like "Given X, prove Y", where you assume "Y is false" and use it to prove "X is false", but X is true, therefore Y has to be true. Sometimes it's easier to do it in that direction than X->Y.


Contrapositive is the fancy word for that technique.

A -> B iff not(B) -> not(A)


As pointed out below, they aren't equivalent.

Compare the output of both when run against "foo bar WIBBLE"


Different behaviour.

capitalize downcases the rest of the each sub-string, the original code did not.


Wow, I just wrote a lengthy reply but I completely missed this. That only adds adds to Ikura's argument though.


> For example, for YouTube alone, users upload over 400 hours of video every minute, which at one gigabyte per hour requires more than one petabyte (1M GB) of new storage every day or about 100x the Library of Congress

Hmm, something up with the sums in the middle of that.

400 hours of video every minute is much more than one gigabyte per hour. It's way more than one terabyte per hour.

Working backwards:-

1 PB/day =~ 42 TB/hour =~ 728 GB/minute


I believe they are saying that the 400 hours they upload every minute are 400GB worth of data.


Ah, yes, good point.


That's only if you're storing one copy of the video.


Variable compression and video resolution?


400 hours video/min = 400 GB/min = 400 x 60 x 24 GB/day = 0.576 PB/day. Close enough.


Another anecdata, but on the other side of the coin:

Virgin cable available right now, BT have put off upgrading my cabinet to FTTC for over 4 years now.

Still, I'm getting ~8Mbps/1MBps so it's hardly a reason to complain.


> That is one of the better lines to ever be written in a legal letter.

Along with: http://www.lettersofnote.com/2013/08/arkell-v-pressdram.html


He's the 6th Brit in space, the 5th man.

> https://www.newscientist.com/article/dn28666-first-official-...

" Despite what you may have heard, Peake is actually the sixth Brit in space. The first was chemist Helen Sharman, who flew to the Russian Mir space station in 1991 as part of Project Juno, a jointly funded mission between a private consortium and Russia. She was followed by the British-born astronauts Michael Foale, Piers Sellers and Nicholas Patrick, who all took US citizenship and flew on NASA missions, and Richard Garriott, a video game developer who went to the ISS as a space tourist. "


> In my books its a minus that you can not rewrite history. What happens if you accidentially add code where you dont own the copyright? Or an API Secret?

Someone will write the necessary scripts (e.g. fossil-rebase) to go into the DB and rewrite history.


> Someone will write the necessary scripts (e.g. fossil-rebase) to go into the DB and rewrite history.

No, they won't. The fossil file format is very strongly protected against any changing of history. Changing history changes multiple hashes (at multiple levels) and breaks it. Immutable history is literally part of the metadata specification, and the db is "just a data store," independent of that specification.


From what I just read, the "shun" method means that you can rewrite history by adding a shun, rebuilding a copy, then switching copies.

Not db rewrite, but the same end result.

edit: bad english


That won't work because the SHA1 hashes won't match up.

If you accidentally check-in proprietary or sensitive content that you didn't mean to publish, you can shun that content. Shunning leaves a hole in your history. There is no way to replace that hole with different content.


Git is the same, if you rebase many hashes will be recalculated, and the "tampering" would be obvious to anyone who had a copy of the repository. It is possible to implement the equivalent of rebase in any distributed VCS, the authors of Fossil simply chose not to. If it becomes more popular, somebody else likely will.


i've been on the fossil dev team since 2008, and i have seen many people claim that it "could" be compromised/modified post facto, and yet... nobody has been able to do it. Fossil's core data model does not just _assume_ that history doesn't change - it makes it essentially impossible to do.

Shunning is a special case which removes a given artifact from the db, but is considered a "nuclear option" of last resort. i've never personally used it.


Yes, but then you are fighting the software, and it wouldnt need to be immutable at all if you can change it anyway


It's a common topic posted by people looking for a big boost of karma.

1. Find the most popular topics (by points) in HN 2. Manually filter out 'event' topics (e.g. product releases, time specific news items, etc) that won't work when reposted 3. Wait until a topic hasn't been raised for a while and post a unique URL (either a related URL that hasn't been posted as a topic but maybe appeared in the discussion, or an existing URL that is made unique) 4. Hope for big boost of karma

Which is why we often see many of the same old subjects being brought up again and again. Not necessarily a bad thing, but I'm sure that some are being posted by people trying to get their karma scores up.

Reminds me, where's that list of pg's essays...



Sound could be an option.

A TV license is required to watch broadcast television, so the number of channels they could be watching is finite. Even a muffled signal detected from a vibrating window (via laser microphone) could be compared to what is currently being broadcast by each of the channels (give or take a short processing delay) and any match found.

Nowadays it's mostly database enforcement. You obviously don't have to care about addresses that do have TV licenses so you just go looking for people with various TV subscriptions (Sky, Virgin Media) that don't have a TV license. It used to be done by the retailers submitting addresses of people who bought/rented TV equipment (TV, VCR, etc), any that didn't get (or already have) a TV license would get a visit shortly afterwards. Also people who watch programmes 'live' on-line (IP -> address conversion thanks to the DSL providers).


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