Re: Proposal: 6NF

"vc" <boston103_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.