I was confused as to how the equation 10 on page 7 or equation 21 on page 8 of this paper http://arxiv.org/abs/1211.1866 was derived. Can someone explain from where does this come and what do the "weird" arrows in Figure 1 on page 7 mean (..it doesn't look like a normal Feynman diagram..)
Especially how does this follow from the Schwinger-Dyson equation?
