I have an undirected, unweighted graph representing a network.
I have a starting node and an end one.
My 'network' is reliable if there is no node such that without that node s and t are not reachable i.e. no node is necessary and all nodes have at least one redundant path.


how can I formally verify this?
thank you



number of totally different path between two nodes in graph theory
If you mean that the network remains connected upon removing any one node, the magic words are "2-vertex-connected graph", or "biconnected graph". An algorithm for determining biconnectivity is described [here](http://garryowen.csisdmz.ul.ie/~cs4115/resources/lect24.pdf), though I am sure there are plenty of other places.


