@article{articlea84e53af,
title   = {Convexity and the finiteness of the number of geodesics: applications to the multiple-image effect},
author = {Giannoni, Fabio and Masiello, Antonio and Piccione, Paolo},
year = {1999},
doi = {10.1088/0264-9381/16/3/008},
journal   = {Classical and Quantum Gravity}
}