Fig. 1

Causal relationship between two nodes expressed by the edge type. Edges ending in an arrow (→) signify activation and edges ending in a bar (⊣) signify inhibition; node x signifies other regulator(s) of B. a A is necessary for B, meaning that whenever A is OFF, B must be OFF, regardless of the state of x; b A is sufficient for B, which means that A being ON implies that B is ON, regardless of the state of x; c A is a necessary inhibitor of B, i.e., A must be ON to inhibit B, implying that when A is OFF, B must be ON, regardless of the state of x; d A is sufficient to inhibit B, i.e., whenever A is ON, B must be OFF, regardless of the state of x; e A is sufficient and necessary for B, i.e., B is always stabilized in the same state as A; f A is a sufficient and necessary inhibitor for B, i.e., B is always stabilized in the state opposite of that of A. Blue edges represent necessary relationships, red edges represent sufficient relationships and black edges represent a sufficient and necessary relationship i.e., when the target node has only one regulator. The corresponding truth table of steady states for each edge type is on the right. States not specified by the logic relationship between A and B, which therefore depend on x, are shown as question marks. The states of A shown in red are the causative states and the states of B shown in red are the resultant states