@article{SF_1975__10_134111,
     author = {J.M. Day},
     title = {Recurrent functions and semigroups.},
     journal = {Semigroup forum},
     pages = {190--202},
     publisher = {mathdoc},
     volume = {10},
     year = {1975},
     zbl = {0299.22002},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__10_134111/}
}