@article{10_4153_CJM_1986_060_5,
     author = {Clarke, Frank H. and Zeidan, Vera},
     title = {Sufficiency and the {Jacobi} {Condition} in the {Calculus} of {Variations}},
     journal = {Canadian journal of mathematics},
     pages = {1199--1209},
     year = {1986},
     volume = {38},
     number = {5},
     doi = {10.4153/CJM-1986-060-5},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1986-060-5/}
}