@article{10_1017_S0017089500005346,
     author = {Robson, J. C.},
     title = {Sums of two regular elements},
     journal = {Glasgow mathematical journal},
     pages = {7--11},
     year = {1984},
     volume = {25},
     number = {1},
     doi = {10.1017/S0017089500005346},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500005346/}
}