@article{10_4153_S0008414X21000547,
     author = {Langford, Jeffrey J.},
     title = {PDE comparison principles for {Robin} problems},
     journal = {Canadian journal of mathematics},
     pages = {108--139},
     year = {2023},
     volume = {75},
     number = {1},
     doi = {10.4153/S0008414X21000547},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008414X21000547/}
}