Waldek,

Thanks for your patient explanation.  So we define

  1/0 = 0

but we do not call this a multiplicative inverse. Should we say then that

  0^(-1)

is still undefined?

Regards,
Bill Page.

On Mon, Mar 28, 2011 at 10:07 AM, you wrote:
>
> Let us recall field axioms:
>
> 1) field is abelian group with respect to addition.  Defining 1/0 = 0
>   does not affect this at all.
> 2) _nonzero_ elements of the field form an abelian group with
>   respect to multiplication.  Again defining 1/0 = 0, because
>   here we consider only nonzero elements (using 1/0 = x with
>   nonzero x would be more tricky)
> 3) distributive law:
>
>   \forall_{a, b, c} a*(b+c) = a*b + a*c
>
>   Since distributive law does not involve division it is satisfied
>   if 1/0 = 0.
>
> The axioms imply \forall_a 0*a = 0.  This is fundamental property
> of fields and means that it is impossible to define 1/0 in such a
> way that _all_ elements of field form multiplicative group.

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