Here in the Metamath proof verification system: http://us.metamath.org/mpegif/1p1e2.html http://us.metamath.org/mpegif/1p1e2.html More interestingly, 2+2=4: ht

Here in the Metamath proof verification system: http://us.metamath.org/mpegif/1p1e2.html http://us.metamath.org/mpegif/1p1e2.html More interestingly, 2+2=4: http://us.metamath.org/mpegif/2p2e4.html http://us.metamath.org/mpegif/2p2e4.html (also have a look at the trivia: http://us.metamath.org/mpeuni/mmset.html#trivia http://us.metamath.org/mpeuni/mmset.html#trivia !)