@article{article69f1b29e,
title   = {Using the variational principle to prove the existence of bound states: a remark},
author = {Perez, José Fernando and Malta, Coraci Pereira and Coutinho, Francisco Antônio Bezerra},
year = {1990},
doi = {10.1119/1.16438},
journal   = {American Journal of Physics}
}