# [Agda] Re: _iff_

Serge D. Mechveliani mechvel at botik.ru
Tue Apr 2 16:56:59 CEST 2013

To my request of

>> [..]
>> And introduce
>>                A iff' B =  (A -> B) \times (B -> A)
>> for this.
>> But can this be written in a nicer way by using Standard library?

Nils Anders Danielsson  wrote on Apr 2 2013

> You may want to use Function.Equivalence._<=>_.

(I copy _<=>_' from the letter on the web page).

> However, this type is defined as a special case of a more general
> definition that uses setoids, and can be somewhat awkward to use.

Well, it works. It is what I asked for.
I have seen  \r=  and  \l=,  and the problem was to guess to grep for
the  \iff  math symbol in the source.

Thanks,

------
Sergei
`