# gcd 0 0 = 0

Simon Peyton-Jones simonpj@microsoft.com
Tue, 18 Dec 2001 01:38:21 -0800

```If everyone likes this I'll put it in; otherwise I'll simply state that
gcd 0 0 is defined to be 0.=20

Christoph does not like this, but the weight of world opinion seems=20
to be fairly clearly in favour of gcd 0 0 =3D 0.    Let's try to wrap =
this
one
up.

Simon

| -----Original Message-----
| From: Alan Bawden [mailto:Alan@LCS.MIT.EDU]=20
| Sent: 17 December 2001 18:45
| Subject: Re: gcd 0 0 =3D 0
|=20
|=20
|    From: Lars Henrik Mathiesen <thorinn@diku.dk>
|    Date: 17 Dec 2001 14:50:21 -0000
|    ...
|    In case it isn't clear already, these definitions make a lattice on
|    the positive integers, with divides ~ leq, gcd ~ meet and=20
| lcm ~ join,
|    using the report's definitions of gcd and lcm.
|=20
| Indeed, that's a nice way of putting it.  How about if the report just
| says:
|=20
|    In order to make the non-negative integers into a lattice=20
| under `gcd'
|    and `lcm', we define `gcd 0 0 =3D 0'.
|=20

```