@article{700848,
     title = {On numerical and non-numerical ecart},
     booktitle = {General Topology and its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1967},
     pages = {236-237},
     zbl = {0171.43602},
     url = {http://dml.mathdoc.fr/item/700848}
}

Kurepa, D. On numerical and non-numerical ecart, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1967), pp. 236-237. http://gdmltest.u-ga.fr/item/700848/