YES(?, 85)

Initial complexity problem:
1:	T:
		(?, 1)    f18(a, b, c, d, e, f) -> f18(a, b + 1, c, d, e, f) [ a >= b + 1 ]
		(?, 1)    f24(a, b, c, d, e, f) -> f24(a, b + 1, c, d, e, f) [ a >= b + 1 ]
		(?, 1)    f31(a, b, c, d, e, f) -> f31(a, b + 1, c, d, e, f) [ a >= b + 1 ]
		(?, 1)    f31(a, b, c, d, e, f) -> f39(a, b, c, d, e, f) [ b >= a ]
		(?, 1)    f24(a, b, c, d, e, f) -> f31(a, 0, c, d, e, f) [ b >= a ]
		(?, 1)    f18(a, b, c, d, e, f) -> f24(a, 0, c, d, e, f) [ b >= a ]
		(1, 1)    f0(a, b, c, d, e, f) -> f18(10, 0, 10, g, 10, h)
	start location:	f0
	leaf cost:	0

Slicing away variables that do not contribute to conditions from problem 1 leaves variables [a, b].
We thus obtain the following problem:
2:	T:
		(1, 1)    f0(a, b) -> f18(10, 0)
		(?, 1)    f18(a, b) -> f24(a, 0) [ b >= a ]
		(?, 1)    f24(a, b) -> f31(a, 0) [ b >= a ]
		(?, 1)    f31(a, b) -> f39(a, b) [ b >= a ]
		(?, 1)    f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
	start location:	f0
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 2 produces the following problem:
3:	T:
		(1, 1)    f0(a, b) -> f18(10, 0)
		(?, 1)    f18(a, b) -> f24(a, 0) [ b >= a ]
		(?, 1)    f24(a, b) -> f31(a, 0) [ b >= a ]
		(?, 1)    f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
	start location:	f0
	leaf cost:	1

A polynomial rank function with
	Pol(f0) = 2
	Pol(f18) = 2
	Pol(f24) = 1
	Pol(f31) = -1
orients all transitions weakly and the transitions
	f24(a, b) -> f31(a, 0) [ b >= a ]
	f18(a, b) -> f24(a, 0) [ b >= a ]
strictly and produces the following problem:
4:	T:
		(1, 1)    f0(a, b) -> f18(10, 0)
		(2, 1)    f18(a, b) -> f24(a, 0) [ b >= a ]
		(2, 1)    f24(a, b) -> f31(a, 0) [ b >= a ]
		(?, 1)    f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
		(?, 1)    f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
	start location:	f0
	leaf cost:	1

A polynomial rank function with
	Pol(f0) = 19
	Pol(f18) = 2*V_1 - 1
	Pol(f24) = 2*V_1 - 1
	Pol(f31) = 2*V_1 - 2*V_2 - 1
orients all transitions weakly and the transition
	f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
strictly and produces the following problem:
5:	T:
		(1, 1)     f0(a, b) -> f18(10, 0)
		(2, 1)     f18(a, b) -> f24(a, 0) [ b >= a ]
		(2, 1)     f24(a, b) -> f31(a, 0) [ b >= a ]
		(19, 1)    f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
		(?, 1)     f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
		(?, 1)     f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
	start location:	f0
	leaf cost:	1

A polynomial rank function with
	Pol(f24) = V_1 - V_2
	Pol(f18) = V_1 - V_2
and size complexities
	S("f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]", 0-0) = 10
	S("f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]", 0-1) = ?
	S("f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]", 0-0) = 10
	S("f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]", 0-1) = ?
	S("f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]", 0-0) = 10
	S("f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]", 0-1) = 19
	S("f24(a, b) -> f31(a, 0) [ b >= a ]", 0-0) = 10
	S("f24(a, b) -> f31(a, 0) [ b >= a ]", 0-1) = 0
	S("f18(a, b) -> f24(a, 0) [ b >= a ]", 0-0) = 10
	S("f18(a, b) -> f24(a, 0) [ b >= a ]", 0-1) = 0
	S("f0(a, b) -> f18(10, 0)", 0-0) = 10
	S("f0(a, b) -> f18(10, 0)", 0-1) = 0
orients the transitions
	f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
	f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
weakly and the transitions
	f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
	f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
strictly and produces the following problem:
6:	T:
		(1, 1)     f0(a, b) -> f18(10, 0)
		(2, 1)     f18(a, b) -> f24(a, 0) [ b >= a ]
		(2, 1)     f24(a, b) -> f31(a, 0) [ b >= a ]
		(19, 1)    f31(a, b) -> f31(a, b + 1) [ a >= b + 1 ]
		(30, 1)    f24(a, b) -> f24(a, b + 1) [ a >= b + 1 ]
		(30, 1)    f18(a, b) -> f18(a, b + 1) [ a >= b + 1 ]
	start location:	f0
	leaf cost:	1

Complexity upper bound 85

Time: 0.174 sec (SMT: 0.164 sec)