  Network rearrangement operations like SNPR (SubNet Prune and Regraft), a
recent generalisation of rSPR (rooted Subtree Prune and Regraft), induce a
metric on phylogenetic networks. To search the space of these networks one
important property of these metrics is the sizes of the neighbourhoods, that
is, the number of networks reachable by exactly one operation from a given
network. In this paper, we present exact expressions for the SNPR neighbourhood
of tree-child networks, which depend on both the size and the topology of a
network. We furthermore give upper and lower bounds for the minimum and maximum
size of such a neighbourhood.
