@article{RCM_1974__8_181624,
     author = {Otto Baessler},
     title = {Observaciones did\'acticas sobre el c\'alculo con n\'umeros ordinales},
     journal = {Revista colombiana de matematicas},
     pages = {191--206},
     publisher = {mathdoc},
     volume = {8},
     year = {1974},
     url = {http://geodesic.mathdoc.fr/item/RCM_1974__8_181624/}
}