@InProceedings{Grave:2006:WF,
    author = {F. Grave and F. Frutos-Alfaro and T. M{\"u}ller and D. Adis},
    title =  {{Wave fronts in General Relativity Theory}},
    booktitle = {Proceedings of the 11th Marcel Grossmann Meeting on General Relativity},
    year = {2006}
}