@article{article9aba04dc,
title   = {Quadratic systems with invariant straight lines of total multiplicity two having Darboux invariants},
author = {Llibre, Jaume and Oliveira, Regilene Delazari dos Santos},
year = {2015},
doi = {10.1142/S0219199714500187},
journal   = {Communications in Contemporary Mathematics}
}