@article{IM_1982__66_142890,
     author = {G.C. Hamrick and David C. Royster},
     title = {Flat {Riemannian} {Manifolds} are {Boundaries.}},
     journal = {Inventiones mathematicae},
     pages = {405--414},
     publisher = {mathdoc},
     volume = {66},
     year = {1982},
     zbl = {0468.57025},
     url = {http://geodesic.mathdoc.fr/item/IM_1982__66_142890/}
}