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If the graph contains a negative-weight cycle reahable from s, however, shortest-path weights are not well defined.
There are infinitely many paths from s to c:
<s,c>, <s,c,d,c>, <s,c,d,c,d,c>, ...
The shortest path from s to c is <s,c>.
There are infinitely many paths from s to e:
<s,e>, <s,e,f,e>, <s,e,f,e,f,e>, ...
Because the cycle <e,f,e> has weight -3, however, there is no shortest path from s to e.