YES(?, 5)

Initial complexity problem:
1:	T:
		(1, 1)    f0(a) -> f5(0)
		(?, 1)    f5(a) -> f5(a + 1) [ 1 >= a ]
		(?, 1)    f5(a) -> f13(a) [ a >= 2 /\ 0 >= b + 1 ]
		(?, 1)    f5(a) -> f13(a) [ a >= 2 ]
	start location:	f0
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 1 produces the following problem:
2:	T:
		(1, 1)    f0(a) -> f5(0)
		(?, 1)    f5(a) -> f5(a + 1) [ 1 >= a ]
	start location:	f0
	leaf cost:	2

A polynomial rank function with
	Pol(f0) = 2
	Pol(f5) = -V_1 + 2
orients all transitions weakly and the transition
	f5(a) -> f5(a + 1) [ 1 >= a ]
strictly and produces the following problem:
3:	T:
		(1, 1)    f0(a) -> f5(0)
		(2, 1)    f5(a) -> f5(a + 1) [ 1 >= a ]
	start location:	f0
	leaf cost:	2

Complexity upper bound 5

Time: 0.073 sec (SMT: 0.070 sec)