Geodesic
An nonstability criterion of equlibrium for nonholonomic system
Theoretical and applied mechanics, Tome 18 (1992) no. 1, p. 21 .

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. 
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     title = {An nonstability criterion of equlibrium for nonholonomic system},
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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/