Basic Networks - Construction Project Scheduling and Control - page 28

The problem in this example is how to draw the preceding logic correctly.
We need to show that activity E depends on both activities B and C, whereas
activity D depends only on activity B. The solution can only be achieved by
using a dummy activity, as shown next. Figures 3.3a and 3.3b are examples
of improper logic. Figure 3.3c shows the proper logic.
Solutions
We can complicate example 3.3 just a little with one change.
(a)
(b)
(c)
Figure 3.3 (a) Improper solution, (b) another improper solution, and (c) proper
solution for example 3.3