B.M. Brown, M. Langer and K.M. Schmidt,
The HELP inequality on trees,
Proc. Sympos. Pure Math. 77 (2008), 337–354
Abstract:
We establish analogues of Hardy and Littlewood's integro-differential
equation for Schrödinger-type operators on metric and discrete
trees, based on a generalised strong limit-point property of the graph Laplacian.