Liao Shantao
Journal of Systems Science and Complexity. 1989, 2(3): 193-227.
Let \mathcal{X} be the linear space of all C~1 vector fields X on a compact n-dimensional C~∞ Riemann manifold(n≥2), endowed with the C~1 norm ‖X‖_1. Write θ(X) for the numberof contractible periodic orbits of X∈\mathcal{X}, which may be finite or infinite. Let \mathcal{X}~* be the set of all X∈\mathcal{X} possessing the property that X has a neighbourhood \mathcal{V} such that every Y∈\mathcal{V} has only a finite number of singularities and at most a countable number of periodic orbits. In this paper, it is shown that any given S∈\mathcal{X}^* has a neighbourhood \mathcal{W} in \mathcal{X} together with a number λ=λ(\mathcal{W})>0 such that θ(X)≤λ for all X∈\mathcal{W}.