Influence network notation. Each influence node x corresponds to 3 chemical species x
2 and four reactions, in a pattern that we call a triplet motif. The solid-edge output of a node x represents the activity of x when activated (i.e., of x
0), while the dashed-edge output (which we have not needed so far) represents the activity of x when inhibited (i.e., of x
2): in that case ‘inhibited’ is not quite the right concept, and we should think of a species x with two states, both having some activity. Activation and inhibition catalyze transitions between x
0 and x
2 through an intermediary x
1 (hollow circles represent catalysis). Each node x can be replaced by its dual ~x without changing the underlying reaction network.