YAP (was Re: Proposal: Remove Show and Eq superclasses of Num)

Tyson Whitehead twhitehead at gmail.com
Tue Oct 18 17:50:12 CEST 2011

On October 17, 2011 19:19:18 Paterson, Ross wrote:
> Balazs Komuves writes:
> > Rings with unity have a canonical map, actually a ring homomorphism (but
> > not necessarily injection) from the integers, namely for the natural
> > integer N, you add together the unit element with itself N times. For
> > negative N, you take the additive inverse.
> > 
> > For fields, you would try to extend this to rationals; however, it seems
> > that because of the non-injectivity of the above, this won't always
> > work. Example: finite fields. In a finite field of order P, we would
> > have f(N/P) = f(N)/f(P) = f(N)/0 which is not defined.
> Good point.  Mind you we already have this with Ratio Int and friends.

Yes.  It doesn't really strike me as such an issue.

Really just another statement that "recip zero" is not defined.

Cheers!  -Tyson

PS:  Thanks for the info on the canonical map Balazs.  Very nice.

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