Fig. 1

Representation of a RN as König multigraph of the corresponding directed hypergraph. Round vertices (with chemical structures shown inside) designate compounds \(x\in X\), while reactions \(r\in R\) are shown as square vertices. Stoichometric coefficients are indicated by the number of edges from x to r for \(s^-_{xr}>0\) and r to x for \(s^+_{xr}>0\), respectively. A flow (an overall reaction) is given by non-negative integer multiples of individual reactions. Here the coefficients \(v_r\) are indicated in the square nodes for each reaction r. The flow shown here defines Oró’s [58] route from HCN to adenine (marked by red triangles) and corresponds to the net reaction \({5 HCN \longrightarrow H5C5N5}\). Figure adapted from [59]