Variational procedure for higher-derivative mechanical models in a fractional integral Cresus F. de L. Godinho, Nelson Panza, José Weberszpil and J. A. Helayël-Neto EPL, 129 6 (2020) 60001 Published online: 13 April 2020 DOI: 10.1209/0295-5075/129/60001