The thing is that (expt 0 0) yields 1 in all three implementations, so no question here. That interesting article mostly discusses this case. And about 0.0^0.0 it says:

"
   As a rule of thumb, one can say that 0^0 = 1 , but 0.0^(0.0) is
undefined, meaning that when approaching from a different direction
there is no clearly predetermined value to assign to 0.0^(0.0) ; but
Kahan has argued that 0.0^(0.0) should be 1, because if f(x), g(x) -->
0 as x approaches some limit, and f(x) and g(x) are analytic
functions, then f(x)^g(x) --> 1


2010/4/29 Malcolm Reynolds <malcolm.reynolds@gmail.com>
I'm not sure about the Lisp standard's view on this, but here is a
variety of reasons why the correct mathematical answer is (arguably)
1, for any combination of integers or floats. I guess this doesn't
answer whether it should be 1.0 or 1 but it definitely shouldn't be an
error.

http://www.faqs.org/faqs/sci-math-faq/specialnumbers/0to0/

Malcolm

On Thu, Apr 29, 2010 at 9:01 PM, Roman Marynchak
<roman.marynchak@gmail.com> wrote:
> Hello,
>
> I have found a tricky issue with EXPT behaviour in different
> implementations.
>
> Namely, evaluating (expt 0.0 0) yields:
>
> 1.0 in SBCL
> 1 in CLISP
> 1.0 in Lispworks.
>
> (expt 0 0.0) results in:
>
> 1.0 in SBCL
> error in CLISP
> error in Lispworks
>
>
> CLHS says that 0^0 = 1, and gives no details about float/integer
> combinations of these zeros.
>
> So, what is the valid answer here? Is there some complex math theory behind
> all this?
>
>
> Regards,
> Roman
>
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