YES(?, 2*a + 2*b + 3)

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

Testing for unsatisfiable constraints removes the following transitions from problem 1:
	eval(a, b) -> eval(a - b, b) [ b >= a + 1 /\ a >= 1 /\ b >= 1 /\ a >= b + 1 ]
	eval(a, b) -> eval(a, b - a) [ a >= b + 1 /\ a >= 1 /\ b >= 1 /\ b >= a ]
We thus obtain the following problem:
2:	T:
		(?, 1)    eval(a, b) -> eval(a - b, b) [ a >= b + 1 /\ a >= 1 /\ b >= 1 ]
		(?, 1)    eval(a, b) -> eval(a, b - a) [ b >= a + 1 /\ a >= 1 /\ b >= 1 /\ b >= a ]
		(1, 1)    start(a, b) -> eval(a, b)
	start location:	start
	leaf cost:	0

A polynomial rank function with
	Pol(eval) = V_1 + V_2 - 1
	Pol(start) = V_1 + V_2 - 1
orients all transitions weakly and the transitions
	eval(a, b) -> eval(a - b, b) [ a >= b + 1 /\ a >= 1 /\ b >= 1 ]
	eval(a, b) -> eval(a, b - a) [ b >= a + 1 /\ a >= 1 /\ b >= 1 /\ b >= a ]
strictly and produces the following problem:
3:	T:
		(a + b + 1, 1)    eval(a, b) -> eval(a - b, b) [ a >= b + 1 /\ a >= 1 /\ b >= 1 ]
		(a + b + 1, 1)    eval(a, b) -> eval(a, b - a) [ b >= a + 1 /\ a >= 1 /\ b >= 1 /\ b >= a ]
		(1, 1)            start(a, b) -> eval(a, b)
	start location:	start
	leaf cost:	0

Complexity upper bound 2*a + 2*b + 3

Time: 0.172 sec (SMT: 0.164 sec)