We may define at this point a one machine problem. In the picture there is an instance with six operations for one machine where the six operations are the nodes, the blue arcs represent the precedences from the source node with the indicated release dates, the red arcs represent a possible sequence for the operations of the machine with the indicated processing times, and the green arcs represent the remaining work with values referring to both the processing times and the remaining work. We may order the operations through a very special heuristic, which we won't describe now. Once we have ordered the operations we find the critical path (indicated as heavy arcs). What is important is that we get from this heuristic a lower bound for the optimal sequence.