 In the deterministic case, the relations of influence between variables can be encoded in a system of structural equations. For illustration, consider again the neuron system we used in  §1.2.1  above to illustrate early preemption. As we saw in  §1.2.3,  for each neuron in the system, we can introduce a variable for whether that neuron fires at the relevant time. Once we’ve done so, the following system of structural equations describes the causal relations between these variables.