Re: Proposal: 6NF
Date: 19 Oct 2006 18:08:24 -0700
Message-ID: <1161306504.907916.306400_at_k70g2000cwa.googlegroups.com>
There seems a very subtle point here which I am currently missing. Or perhaps the terminology is being used in two subtly different ways? Either way I am vexed, as from a certain angle you both appear to be right.
On Oct 20, 1:18 am, Gene Wirchenko <g..._at_ocis.net> wrote:
> "vc" <boston..._at_hotmail.com> wrote:
> >JOG wrote:[snip]
>
> >> As far as I understood from my school years, an operation just mapped
> >> one set of values to another. I remain unconvinced of the need for an
> >> operation upon a set to map to itself.
>
> >f:SxS -> S is not "a set to map to itself". We are talking here about The page you suggested sure seems to say that though!
>
> >very very basic stuff that's known if not from the primary school then
> >at least from the secondary school agebra (or at least should be).
>
> >>Where is such a definition? As I
> >> said, I am open to convincing, but I was not aware of such a
> >> pre-requisite for closure?
>
> >If books are not read any more nowadays, then this might help:
>
> >http://mathworld.wolfram.com/BinaryOperation.html Look at clause 2.
>
> "Binary Operation
>
> A binary operation f(x,y) is an operation that applies to two
> quantities or expressions x and y.
>
> A binary operation on a nonempty set A is a map f:AxA->A such that
>
> 1. f is defined for every pair of elements in A, and
>
> 2. f uniquely associates each pair of elements in A to some element of
> A.
>
> Examples of binary operation on A from AxA to A include addition (+),
> subtraction (-), multiplication (x) and division (÷)."
>
> Sincerely,
>
> Gene Wirchenko
>
> Computerese Irregular Verb Conjugation:
> I have preferences.
> You have biases.
> He/She has prejudices.
Received on Fri Oct 20 2006 - 03:08:24 CEST