You kind of need to understand the Hy synax for list and dict comprehensions, but with your rainbow bracket coloring on, code like this grows by thinking in code like this. What, if I was on a dumber language, I might have been neck-deep in double loops already; indeed, much of the conceptual footwork to give us this functionality has been done by Python who came with (the Pythonic version of) list comprehensions (which yes, were in Haskell before). But look how messed up `cross_dict` gets in Python: