Re: [gentoo-user] Portage 2.2

[Alan McKinnon <alan.mckinnon@gmail.com>]

On 24/07/2013 22:15, gottlieb@nyu.edu wrote:
> On Wed, Jul 24 2013, Willie WY Wong wrote:
> 
>> Speaking as a mathematician (and A. Gottlieb will agree with me), I
>> would be rather annoyed that they chose (if this is not a misquote 
>> from the original proposed documentation) to use '/' for set 
>> difference instead of '\' as it is supposed to be. 
> 
> I was also surprised to see `/'.  A part of me was going to send about
> quotient groups (the normal usage of '/') but I managed to refrain
> myself.  However, now that willie has opened the door ...
> 
> / is normally used for quotients.  For example, if we take the group Z
> of integers under addition and the subgroup 2Z of the even integers,
> then Z / 2Z is the quotient that results from taking Z and identifying
> all the elements of 2Z.  So in Z / 2Z, all the even integers are zero
> and hence all odd integers are equivalent (since they differ by even
> integers, which are zero).  Thus the quotient has only 2 elements and is
> the familiar group Z2, the integers mod 2.
> 
> The above can be generalized.
> 
> allan
> 

In portage's defense, the symbol used is not really mathematical
notation, it's an operator used in code, and only in code.

We do this lots:

* is multiplication
^ is exponentiation
% is modulus (sometimes just mod)

and several more, all driven by the lack of appropriate symbols on early
ASCII keyboards (and the majority of current keyboards...)

I would probably have selected "/" as well if I were the implementer,
but that's because I heavily resist using backslash for anything other
than escapes. My brain usually will not let me go against this one...

You mathematician chaps could probably resolve this one nicely for
yourselves by treating it as just another mangle by Applied
Mathematicians      <====== joke   :-)


-- 
Alan McKinnon
alan.mckinnon@gmail.com