Bertfried Fauser wrote:
>
> >> > ? ? ? prime?: % -> Boolean
> >> > ? ? ? ? ? ? ++ prime?(x) tests if x can never be written as the product
> >> > of two
> >> > ? ? ? ? ? ? ++ non-units of the ring,
> >> > ? ? ? ? ? ? ++ i.e., x is an irreducible element.
>
> * Given this definition, why should -5=(-1)*5 be a prime at all?
-1 is a unit (= invertible element)...
> * given prime? uses a statistical method, the definition is also not
> met and should possibly be stated as:
> ++ prime?(x) tests if x can not be written as the product of two
> ++ non-units of the ring (with very small probability)
>
This is similar to '+' and '*' in Float: both give approximate
result but we still claim that Float is a Field, and do not put
disclaimer in AbelianGroup (and SemiGroup)...
--
Waldek Hebisch
[email protected]
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