@article {boscaggin2012one, title = {One-signed harmonic solutions and sign-changing subharmonic solutions to scalar second order differential equations}, journal = {Advanced Nonlinear Studies}, volume = {12}, number = {3}, year = {2012}, pages = {445{\textendash}463}, publisher = {Advanced Nonlinear Studies, Inc.}, doi = {10.1515/ans-2012-0302}, author = {Alberto Boscaggin} }