I am trying to read a paper on Algebraic Topology and Concurrency (doi: 10.1016/j.tcs.2006.03.022), which claims to make use of Dijkstra's notation in talking about concurrency. Specifically, I am trying to understand the following lines, where $a,b,c$ are sephamores, and P and V are the locking and unlocking operations, respectively.
A=Pa.(Pb.Vb.Pc.Vc)*.Va
B=Pc.Pb.Vc.Pa.Va.Vb
PROG=A|B
What do the above lines mean? Specifically, what does the * mean in line 1, and line 3 in its entirety?