@misc{RCM_2009_43_2_a1,
     title = {Una demostraci\'on alternativa del teorema de ultral{\'\i}mites},
     journal = {Revista colombiana de matematicas},
     pages = {115--138},
     publisher = {mathdoc},
     volume = {43},
     number = {2},
     year = {2009},
     url = {http://geodesic.mathdoc.fr/item/RCM_2009_43_2_a1/}
}