3 ms·
Compare a proof in a text book or most papers with this: http://us.metamath.org/mpegif/mmset.html http://us.metamath.org/mpegif/mmset.html
by jk4930 10y ago
Compare a proof in a text book or most papers with this: http://us.metamath.org/mpegif/mmset.html http://us.metamath.org/mpegif/mmset.html