Clearly, L(1) = 0, and we assume that L(n) = 0 < 1.6708n for n 0. We will prove by induction that L(n) 1.6708n.
Assume that this induction hypothesis is true on all chordal graphs with at most n − 1 vertices. We will show that this
leads to L(n) 1.6708n for each of the inequalities above.
For inequality 1, we need to verify that 4 · 1.6708n−3 1.6708n, which amounts to observing that 4 1.67083 ≈ 4.6642.
For inequality 2, we need to verify that 5·1.6708n−4 +1.6708n−2 1.6708n, which amounts to observing that 5 1.67084 −
1.67082 ≈ 5.0013. As 4L(n − 4) + L(n − 2) 5L(n − 4) + L(n − 2), we immediately obtain the bound for inequality 5. For
inequality 3, we need to verify that t · 1.6708n−t + 1.6708n−1 1.6708n, which amounts to observing that t 1.6708t −
1.6708t−1, for all t 5. Because (t − 1)L(n − t) + L(n − 1) tL(n − t) + L(n − 1), we have the bound for inequality 6 as
well. For inequalities 4 and 8, we observe that if t 2 then L(n) L(n − t) + L(n − 1) L(n − 2) + L(n − 1), and we need
to verify that 1.6708n−2 + 1.6708n−1 1.6708n, which amounts to observing that 1 + 1.6708 = 2.6708 1.67082 ≈ 2.7916.
Finally, for inequalities 6 and 9, we have L(n) tL(n − t) (t + 1)L(n − t), and we verify that (t + 1) · 1.6708n−t 1.6708n,
by observing that t + 1 1.6708t
, for all t 3. ✷
4. Concluding remark
Clearly, L(1) = 0, and we assume that L(n) = 0 < 1.6708n for n 0. We will prove by induction that L(n) 1.6708n.
Assume that this induction hypothesis is true on all chordal graphs with at most n − 1 vertices. We will show that this
leads to L(n) 1.6708n for each of the inequalities above.
For inequality 1, we need to verify that 4 · 1.6708n−3 1.6708n, which amounts to observing that 4 1.67083 ≈ 4.6642.
For inequality 2, we need to verify that 5·1.6708n−4 +1.6708n−2 1.6708n, which amounts to observing that 5 1.67084 −
1.67082 ≈ 5.0013. As 4L(n − 4) + L(n − 2) 5L(n − 4) + L(n − 2), we immediately obtain the bound for inequality 5. For
inequality 3, we need to verify that t · 1.6708n−t + 1.6708n−1 1.6708n, which amounts to observing that t 1.6708t −
1.6708t−1, for all t 5. Because (t − 1)L(n − t) + L(n − 1) tL(n − t) + L(n − 1), we have the bound for inequality 6 as
well. For inequalities 4 and 8, we observe that if t 2 then L(n) L(n − t) + L(n − 1) L(n − 2) + L(n − 1), and we need
to verify that 1.6708n−2 + 1.6708n−1 1.6708n, which amounts to observing that 1 + 1.6708 = 2.6708 1.67082 ≈ 2.7916.
Finally, for inequalities 6 and 9, we have L(n) tL(n − t) (t + 1)L(n − t), and we verify that (t + 1) · 1.6708n−t 1.6708n,
by observing that t + 1 1.6708t
, for all t 3. ✷
4. Concluding remark
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