YES(?, 25)

Initial complexity problem:
1:	T:
		(?, 1)    f4(a) -> f5(a) [ 0 >= b + 1 ]
		(?, 1)    f4(a) -> f5(a)
		(1, 1)    f0(a) -> f4(0)
		(?, 1)    f5(a) -> f11(a) [ a >= 3 ]
		(?, 1)    f4(a) -> f11(a)
		(?, 1)    f5(a) -> f4(a + 1) [ 2 >= a ]
		(?, 1)    f11(a) -> f14(a) [ 1 >= a ]
		(?, 1)    f11(a) -> f14(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)    f4(a) -> f5(a) [ 0 >= b + 1 ]
		(?, 1)    f4(a) -> f5(a)
		(1, 1)    f0(a) -> f4(0)
		(?, 1)    f5(a) -> f4(a + 1) [ 2 >= a ]
	start location:	f0
	leaf cost:	4

A polynomial rank function with
	Pol(f4) = -2*V_1 + 6
	Pol(f5) = -2*V_1 + 5
	Pol(f0) = 6
orients all transitions weakly and the transition
	f5(a) -> f4(a + 1) [ 2 >= a ]
strictly and produces the following problem:
3:	T:
		(?, 1)    f4(a) -> f5(a) [ 0 >= b + 1 ]
		(?, 1)    f4(a) -> f5(a)
		(1, 1)    f0(a) -> f4(0)
		(6, 1)    f5(a) -> f4(a + 1) [ 2 >= a ]
	start location:	f0
	leaf cost:	4

Repeatedly propagating knowledge in problem 3 produces the following problem:
4:	T:
		(7, 1)    f4(a) -> f5(a) [ 0 >= b + 1 ]
		(7, 1)    f4(a) -> f5(a)
		(1, 1)    f0(a) -> f4(0)
		(6, 1)    f5(a) -> f4(a + 1) [ 2 >= a ]
	start location:	f0
	leaf cost:	4

Complexity upper bound 25

Time: 0.118 sec (SMT: 0.114 sec)