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

Initial complexity problem:
1:	T:
		(1, 1)    f2(a, b, c, d) -> f300(a, b, c, d)
		(?, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ e >= 1 /\ b >= a + 1 ]
		(?, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ 0 >= e + 1 /\ b >= a + 1 ]
		(?, 1)    f300(a, b, c, d) -> f300(a, b - 1, 0, d) [ b >= a + 1 ]
		(?, 1)    f300(a, b, c, d) -> f1(a, b, c, e) [ a >= b ]
	start location:	f2
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 1 produces the following problem:
2:	T:
		(1, 1)    f2(a, b, c, d) -> f300(a, b, c, d)
		(?, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ e >= 1 /\ b >= a + 1 ]
		(?, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ 0 >= e + 1 /\ b >= a + 1 ]
		(?, 1)    f300(a, b, c, d) -> f300(a, b - 1, 0, d) [ b >= a + 1 ]
	start location:	f2
	leaf cost:	1

A polynomial rank function with
	Pol(f2) = -V_1 + V_2
	Pol(f300) = -V_1 + V_2
orients all transitions weakly and the transitions
	f300(a, b, c, d) -> f300(a + 1, b, e, d) [ e >= 1 /\ b >= a + 1 ]
	f300(a, b, c, d) -> f300(a + 1, b, e, d) [ 0 >= e + 1 /\ b >= a + 1 ]
	f300(a, b, c, d) -> f300(a, b - 1, 0, d) [ b >= a + 1 ]
strictly and produces the following problem:
3:	T:
		(1, 1)        f2(a, b, c, d) -> f300(a, b, c, d)
		(a + b, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ e >= 1 /\ b >= a + 1 ]
		(a + b, 1)    f300(a, b, c, d) -> f300(a + 1, b, e, d) [ 0 >= e + 1 /\ b >= a + 1 ]
		(a + b, 1)    f300(a, b, c, d) -> f300(a, b - 1, 0, d) [ b >= a + 1 ]
	start location:	f2
	leaf cost:	1

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

Time: 0.158 sec (SMT: 0.149 sec)