@article{JGG_2009_13_1_JGG_2009_13_1_a10,
     author = {C. Leopold },
     title = {Virtual and {Real} {Geometry} {Learning} {Environments}},
     journal = {Journal for geometry and graphics},
     pages = {121--13},
     publisher = {mathdoc},
     volume = {13},
     number = {1},
     year = {2009},
     url = {http://geodesic.mathdoc.fr/item/JGG_2009_13_1_JGG_2009_13_1_a10/}
}