@conference{Tra-Des-Fay-2009-1,
    author={Mathieu Trampont and C. Destré and Alain Faye },
    title={Solving a hierarchical network design problem with two 
           stabilized column generation approaches },
    publisher={International Network Optimization Conference, Pisa, },
    year={2009 },
    month={4},
    pages={6},
}