Thanks Wren. That was my guess too, but it seems not necessary: <a href="http://stackoverflow.com/questions/12103309/when-is-a-composition-of-catamorphisms-a-catamorphism" target="_blank">http://stackoverflow.com/questions/12103309/when-is-a-composition-of-catamorphisms-a-catamorphism</a><div>
<br><div class="gmail_quote">On Sat, Aug 25, 2012 at 10:33 PM, wren ng thornton <span dir="ltr"><<a href="mailto:wren@freegeek.org" target="_blank">wren@freegeek.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>On 8/24/12 3:44 AM, Sebastien Zany wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
More specifically (assuming I understood the statement correctly):<br>
<br>
Suppose I have two base functors F1 and F2 and folds for each: fold1 :: (F1<br>
a -> a) -> (μF1 -> a) and fold2 :: (F2 a -> a) -> (μF2 -> a).<br>
<br>
Now suppose I have two algebras f :: F1 μF2 -> μF2 and g :: F2 A -> A.<br>
<br>
When is the composition (fold2 g) . (fold1 f) :: μF1 -> A a catamorphism?<br>
</blockquote>
<br></div>