A fixed-parameter algorithm for the directed feedback vertex set problem

@article{Chen2008AFA,
  title={A fixed-parameter algorithm for the directed feedback vertex set problem},
  author={Jianer Chen and Yang Liu and Songjian Lu and Barry O’Sullivan and Igor Razgon},
  journal={J. ACM},
  year={2008},
  volume={55},
  pages={21:1-21:19}
}
The (parameterized) FEEDBACK VERTEX SET problem on directed graphs (i.e., the DFVS problem) is defined as follows: given a directed graph <i>G</i> and a parameter <i>k</i>, either construct a feedback vertex set of at most <i>k</i> vertices in <i>G</i> or report that no such a set exists. It has been a well-known open problem in parameterized computation and complexity whether the DFVS problem is fixed-parameter tractable, that is, whether the problem can be solved in time <i>f</i>(<i>k</i>)<i… 

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