[Haskell-cafe] Category Theory woes
Alexander Solla
ajs at 2piix.com
Thu Feb 18 15:20:34 EST 2010
On Feb 18, 2010, at 10:19 AM, Nick Rudnick wrote:
> Back to the case of open/closed, given we have an idea about sets --
> we in most cases are able to derive the concept of two disjunct sets
> facing each other ourselves, don't we? The only lore missing is just
> a Bool: Which term fits which idea? With a reliable terminology
> using «bordered/unbordered», there is no ambiguity, and we can pass
> on reading, without any additional effort.
There are sets that only partially contain their boundary. They are
neither open nor closed, in the usual topology. Consider (0,1] in the
Real number line. It contains 1, a boundary point. It does not
contain 0. It is not an open set OR a closed set in the usual
topology for R.
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