(defmodule leap
  (export (leap-year 1)))

(defun leap-year
  ([year] (when (=:= (rem year 400) 0))
   'true)
  ([year] (when (=:= (rem year 100) 0))
   'false)
  ([year] (when (=:= (rem year 4) 0))
   'true)
  ([_]
   'false))

Add default introductory code example
Add default introductory code example

Instead of having logic for a fallback in the backend, we're choosing a
default for the snippet file.

For tracks that have core exercises, we pick the first core exercise.
For tracks without these, we pick the first exercise listed in the config.

Note that we're aiming for 10 lines and a max-width of 40 columns.
This solution has 12 lines, so we may want to adjust it.
