definition-edge cut is the set of edges which disconnect the graph if we remove it from the edge set of the graph.
How are these two definitions equivalent?
definition-edge cut is the set of edges which disconnect the graph if we remove it from the edge set of the graph.
How are these two definitions equivalent?
On
They are not completely equivalent -- for example, consider
5
/ \
1---2---3---4
The set $\{23\}$ is an edge cut according to both definitions (take $S=\{1,2\}$, for example).
The second definition appears to allow $\{23,34\}$ to be an edge cut: removing those edges certainly disconnects the graph. I don't think it is standard to consider $\{23,34\}$ a cut, however -- the definition should be that it is a minimal set of edges whose removal will disconnect the graph.
The first definition defines that if you can divide your graph into two disjoint sets of vertexes. And the edge-cut as the set of edges that connect these two sets of vertexes.
The second definition defines and edge cut as a set of edges that would disconnect these two sets of vertexes.