@article{M2AN_2009__43_1_119_0,
     author = {Ditkowski, Adi},
     title = {Mathematical analysis of the optimizing acquisition and retention over time problem},
     journal = {ESAIM: Mod\'elisation math\'ematique et analyse num\'erique},
     pages = {119--137},
     publisher = {EDP-Sciences},
     volume = {43},
     number = {1},
     year = {2009},
     doi = {10.1051/m2an:2008043},
     mrnumber = {2494796},
     zbl = {1156.91432},
     language = {en},
     url = {http://www.numdam.org/articles/10.1051/m2an:2008043/}
}