YES(?, a + 2)

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

Repeatedly propagating knowledge in problem 1 produces the following problem:
2:	T:
		(?, 1)    eval(a, b) -> eval(a - 1, b) [ a >= 1 /\ b >= a ]
		(1, 1)    eval(a, b) -> eval(b, b) [ a >= 1 /\ a >= b + 1 ]
		(1, 1)    start(a, b) -> eval(a, b)
	start location:	start
	leaf cost:	0

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

Complexity upper bound a + 2

Time: 0.090 sec (SMT: 0.086 sec)