This paper: http://kam.mff.cuni.cz/~fiala/tw.pdf http://kam.mff.cuni.cz/~fiala/tw.pdf gives a deeper (but still very comprehensible) overview look at corollary

This paper: http://kam.mff.cuni.cz/~fiala/tw.pdf http://kam.mff.cuni.cz/~fiala/tw.pdf gives a deeper (but still very comprehensible) overview look at corollary 2.5 and for more specifics.