1) How many distinct SYN-sequences are there for the program
Thread 1      Thread 2       Thread 3
p2.send(a)    x=p2.recv()    p2.send(d)
x=p1.recv()   y=p2.recv()    p1.send(e)
y=p1.recv()   p1.send(b)
z=p1.recv()   p1.send(c)


You don't have to draw a diagram for each, draw a few and show how you can
reach the solution

Answer: 6

2) What assumptions do we have to make to ensure that we only need to
execute each SYN-sequence once?

Answer: Consider all possible things that can affect a concurrent program's
output.

3) What is the state explosion problem. Construct a simple example that show
the number of states can grow exponentially with respect to the number of
statements.

Answer: Make independent short snippets, each can double the number of
states