Non-wandering points and the depth for graph maps

Let G be a graph and f:G→G be continuous.Denote by R（f） andΩ（f） the set of recurrent points and the set of non-wandering points of f respectively.LetΩ（f） = G andΩ（f）=Ω(f|Ω（f）)) for all n∈N.The minimal m∈NU {∞} such thatΩ（f）=Ω（f） is called the depth of f.In this paper,we show thatΩ（f）=（?） and the depth of f is at most 2.Furthermore,we obtain some properties of non-wandering points of f.