On Sun, Apr 6, 2008 at 7:52 PM, Kelly Jones <[EMAIL PROTECTED]>
wrote:
> Many programming languages (including Perl, Ruby, and PHP) support hashes:
>
> $color['apple'] = 'red';
> $color['ruby'] = 'red';
>
> $type['apple'] = 'fruit';
> $type['ruby'] = 'gem';
>
> This quickly lets me find the color
(sorry I just hit send on a blank email; I'm absent-minded)
First, in the strictest mathematical sense, a relation from a set $a to a
set $b is a subset of the cross-product $a x $b.
(obviously, the mathematical notation is not a great way to represent this
in a program.)
Hence, a relation is a
