Variables: 
chan[1]: "X.b" 
chan[2]: "Y.b" 
chan[3]: "Z.b" 

Event graph: 
event[0]: fork: null, #pred: 0, succ: 1 2 3 

# process[1]:
event[1]: send: X.b!(123), pid: 1, #pred: 1, succ: 1 
channel deps: 1 

# process[2]:
event[2]: send: Y.b!(456), pid: 2, #pred: 1, succ: 2 
channel deps: 2 

# process[3]:
event[3]: send: Z.b!(789), pid: 3, #pred: 1, succ: 3 
channel deps: 3 

