[Haskell-cafe] Category Theory woes

Nick Rudnick joerg.rudnick at t-online.de
Sat Feb 20 13:34:46 EST 2010

A place in the hall of fame and thank you for mentioning clopen... ;-)

Just wanting to present open/closed as and example of improvable maths 
terminology, I oversaw this even more evident defect in it and even 
copied it into my improvement proposal, bordered/unbordered:

It is questionable style to name two properties, if they can occur 
combined, as an antagonistic pair...!

Acccordingly, it is more elegant to draw such terms from independent 

This subject seems to drive me crazy... I actually pondered on 
improvement, and came to:

«faceless» in replacement of «open»

Rough explanation: The «limit» of a closed set can by the limit of 
another closed set that may even share only this limit -- a faceless set 
has -- under the given perspective -- no such part to «face» to beyond. 
Any comments?

But the big question is now: What (non antagonistic) name can be found 
for the other property??

Any ideas...??



Ergonomic terminology comes not for free, giving a quick answer here 
would be «maths style» with replacing

Michael Matsko wrote:
> Nick,
>     Actually, clopen is a set that is both closed and open.  Not one 
> that is neither.  Except in the case of half-open intervals, I can't 
> remember talking much in topology about sets with a partial boundary.

Alexander Solla wrote:
> Clopen means a set is both closed and open, not that it's "partially 
> bordered".

Daniel Fischer wrote:
> And we'd be very wrong. There are sets which are simultaneously open and 
> closed. It is bad enough with the terminology as is, throwing in the 
> boundary (which is an even more difficult concept than open/closed) would 
> only make things worse.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20100220/1164b04d/attachment.html

More information about the Haskell-Cafe mailing list