@article{10_4153_CJM_1976_064_x,
     author = {Tromba, A. J.},
     title = {Almost-Riemannian {Structures} on {Banach} {Manifolds:} {The} {Morse} {Lemma} and the {Darboux} {Theorem}},
     journal = {Canadian journal of mathematics},
     pages = {640--652},
     year = {1976},
     volume = {28},
     number = {3},
     doi = {10.4153/CJM-1976-064-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1976-064-x/}
}