@article{de castro_2023,  title={Close relation between the integrating factor and the Green function for first-order differential equations},  volume={45},  ISSN={1806-1117},  url={https://doi.org/10.1590/1806-9126-RBEF-2023-0052},  DOI={10.1590/1806-9126-RBEF-2023-0052},  journal={Revista Brasileira de Ensino de Física},  publisher={Sociedade Brasileira de Física - SBF},  author={de Castro, Antonio S.},  year={2023},  pages={e20230052} }