2+2=4

[void4]

The proof of 2+2=4 down to the axioms of mathematics:

(the final node is in the top right corner)

http://us.metamath.org/mpeuni/2p2e4.html

http://us.metamath.org/mpeuni/mmset.html#trivia

Another visualization as concentric rings, with the proof of 2p2e4 in the center. The most outlying dependencies have no dependencies (axioms), and each level further in only depends on proofs on the outer shells.