More specifically (assuming I understood the statement correctly):

Suppose I have two base functors F1 and F2 and folds for each: fold1 :: (F1 a -> a) -> (ìF1 -> a) and fold2 :: (F2 a -> a) -> (ìF2 -> a).

Now suppose I have two algebras f :: F1 ìF2 -> ìF2 and g :: F2 A -> A.

When is the composition (fold2 g) . (fold1 f) :: ìF1 -> A a catamorphism?

On Thu, Aug 23, 2012 at 10:11 PM, Sebastien Zany <sebastien@chaoticresearch.com> wrote:
From page 3 of http://research.microsoft.com/en-us/um/people/emeijer/Papers/meijer94more.pdf:

it is not true in general that catamorphisms are closed under composition

When is this true?