Positive feedback motif: original reaction graph and dense realization structure. (a) This subfigure shows the reaction graph of a gene regulation network model with positive feedback described originally in  and used in Example 1. (b) This subfigure shows all the mathematically possible reactions that can result in the same dynamical behaviour as the original biologically meaningful network shown in Figure 1. The core-reactions in the dense realization are shown with solid arrows, while the non-core reactions are indicated by dashed arrows.
Szederkényi et al. BMC Systems Biology 2011 5:177 doi:10.1186/1752-0509-5-177