Published online by Cambridge University Press: 07 September 2017
Let $M$ be an analytic connected 2-manifold with empty boundary, over the ground field
$\mathbb{F}=\mathbb{R}$ or
$\mathbb{C}$. Let
$Y$ and
$X$ denote differentiable vector fields on
$M$. We say that
$Y$ tracks
$X$ if
$[Y,X]=fX$ for some continuous function
$f:\,M\rightarrow \mathbb{F}$. A subset
$K$ of the zero set
$\mathsf{Z}(X)$ is an essential block for
$X$ if it is non-empty, compact and open in
$\mathsf{Z}(X)$, and the Poincaré–Hopf index
$\mathsf{i}_{K}(X)$ is non-zero. Let
${\mathcal{G}}$ be a finite-dimensional Lie algebra of analytic vector fields that tracks a non-trivial analytic vector field
$X$. Let
$K\subset \mathsf{Z}(X)$ be an essential block. Assume that if
$M$ is complex and
$\mathsf{i}_{K}(X)$ is a positive even integer, no quotient of
${\mathcal{G}}$ is isomorphic to
$\mathfrak{s}\mathfrak{l}(2,\mathbb{C})$. Then
${\mathcal{G}}$ has a zero in
$K$ (main result). As a consequence, if
$X$ and
$Y$ are analytic,
$X$ is non-trivial, and
$Y$ tracks
$X$, then every essential component of
$\mathsf{Z}(X)$ meets
$\mathsf{Z}(Y)$. Fixed-point theorems for certain types of transformation groups are proved. Several illustrative examples are given.