@article {Forms1963,
title = {Forms of Engel Functions},
year = {1963},
notes = {https://doi.org/10.2307/1909167},
url = {https://www.esri.ie/publications/forms-of-engel-functions},
author = {Leser, C.},
journal = {Econometrica, Vol. 31 No. 4, October 1963},
}