No event pending on `a'.
No event pending on `b'.
No event pending on `c'.
expect pending event on a, not b 
queue:	0	a : 0
No event pending on `b'.
time: 0
	0	a : 0
No event pending on `a'.
queue:	10	b : 1	[from a:=0]
time: 5
	10	b : 1	[by a:=0]
	20	c : 0	[by b:=1]
No event pending on `a'.
No event pending on `b'.
No event pending on `c'.
time: 20
