I agree that the first formulation is a bit incomprehensible, though two-liner breadth-first search is understandable if a bit amazing. Some of the latter vers

I agree that the first formulation is a bit incomprehensible, though two-liner breadth-first search is understandable if a bit amazing. Some of the latter versions (and perhaps ultimately the very last version) are easier to walk through for a beginner, though, and are calculated from properties expressed in the first.