Over the days after Kendrick Lamar suddenly released “The Heart Part 4,” I found myself having passionate arguments with friends about which section we liked the most. At nearly five minutes long, the song has at least four distinct parts. It’s a schizophrenic collection of each one of Lamar’s identities. And together it becomes a stunning cross-section of what he can do—almost as if when he clearly spells out that he is “The. Grea-test. Rap-per a-live,” the song’s macro construction itself is the proof.