[Agda] Decidable _\~~_ of Semiring

[Serge D. Mechveliani]

On Fri, Nov 09, 2012 at 09:35:49AM -0500, Daniel Peebles wrote:
> As with everything, you can just click on Decidable in the hyperlinked HTML
> documentation to find out where the declaration you want is. 
> [..]

I see the Agda Reference manual:
  http://wiki.portal.chalmers.se/agda/pmwiki.php?n=ReferenceManual.TOC,

it is helpul. But it is on the _language_я.
Where to find a similar doc on the Standard library?
(for example, the  Decidable  thing is of the library).

Thanks,

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Sergei