> Isn't it just that backpropagation on the layered topology is relatively straightforward? That's not to say you can't write a backpropagation on an arbitrary

> Isn't it just that backpropagation on the layered topology is relatively straightforward? That's not to say you can't write a backpropagation on an arbitrary digraph... Moreover, any arbitrary digraph can be expressed as a layered topology (possibly with a lot of 0-weights). Since there's no fundamental difference you might as well work with whatever's easiest to compute with.