@article{AFM_1996_21_1_a1,
     author = {Bent Fuglede},
     title = {Harmonic morphisms between semi-riemannian manifolds},
     journal = {Annales Fennici Mathematici},
     pages = {31--50},
     publisher = {mathdoc},
     volume = {21},
     number = {1},
     year = {1996},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AFM_1996_21_1_a1/}
}