<div dir="ltr">Refl, I believe.</div><br><div class="gmail_quote"><div dir="ltr">On Thu, Jan 14, 2016 at 1:56 PM Andreas Abel <<a href="mailto:andreas.abel@ifi.lmu.de">andreas.abel@ifi.lmu.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">What does this smiley :~: stand for?<br>
<br>
On 13.01.2016 06:58, David Feuer wrote:<br>
> These are not likely to be *useful*, but they fall easily into the<br>
> general bucket of "exactly one sensible instance exists".<br>
><br>
> instance Semigroup (a :~: b) where<br>
>    r <> _ = r<br>
><br>
> instance a ~ b => Monoid (a :~: b) where<br>
>    mempty = Refl<br>
>    mappend r _ = r<br>
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><br>
<br>
<br>
--<br>
Andreas Abel  <><      Du bist der geliebte Mensch.<br>
<br>
Department of Computer Science and Engineering<br>
Chalmers and Gothenburg University, Sweden<br>
<br>
<a href="mailto:andreas.abel@gu.se" target="_blank">andreas.abel@gu.se</a><br>
<a href="http://www2.tcs.ifi.lmu.de/~abel/" rel="noreferrer" target="_blank">http://www2.tcs.ifi.lmu.de/~abel/</a><br>
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</blockquote></div>