Before revision: Boolean networks are discrete dynamical systems in which the state (zero or one) of each network node at time t is updated to a state determined by the states at time t-1 of those nodes that have links to it.
After revision: Boolean networks are discrete dynamical systems in which the state (zero or one) of each node is updated at each time t to a state determined by the states at time t-1 of those nodes that have links to it.