Geodesic
An nonstability criterion of equlibrium for nonholonomic system
Theoretical and applied mechanics, Tome 18 (1992) no. 1, p. 21 
Ranislav Bulatović. An nonstability criterion of equlibrium for nonholonomic system. Theoretical and applied mechanics, Tome 18 (1992) no. 1, p. 21 . http://geodesic.mathdoc.fr/item/TAM_1992_18_1_a2/
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     author = {Ranislav Bulatovi\'c},
     title = {An nonstability criterion of equlibrium for nonholonomic system},
     journal = {Theoretical and applied mechanics},
     pages = {21 },
     year = {1992},
     volume = {18},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAM_1992_18_1_a2/}
}
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Voir la notice de l'article provenant de la source eLibrary of Mathematical Institute of the Serbian Academy of Sciences and Arts

Let $\Pi(\mathbf q)=\Pi_k(\mathbf q)+\Pi_{k+1}(\mathbf q)+\dots$, $\Pi_k(\mathbf q)\geq2$ and $A(\mathbf q)=A_0+A_s(\mathbf q)+\dots$, $s>1$, be McLaurin series of analytic potential and vector matrix of nonholonomic constraints. It can be proved that if there exist unit vector $\mathbf e\in R^n\{\mathbf q\}$ for which conditions $A^T_0e=0$, $\Pi_k(\mathbf e)=0$ and $\Pi_{k+1}(\mathbf e)0$ are satisfied, then the equilibrium $\mathbf q=\bar{\mathbf q}=0$ is nonstable.