[PRL] IOP and disjoint unions

[William D Clinger]

Doug wrote:
> > Obviously A+A is not equivalent to A in category theory.
> 
> I don't get this.  I don't know anything about category theory, but it
> seems like "an apple or an apple" is always the same as "an apple".

It is, for a suitable definition of "or" that has little if
anything to do with the disjoint union signified by the plus
sign above.  (See subject line.)

> (Whereas "an apple and an apple" is not.)  Or are you saying that
> A = A might not be true?  (Don't tell Ayn Rand...)

I don't think she'd listen to me anyway.  This has somewhat
to do with logic...

Will