Published online by Cambridge University Press: 07 September 2017
Let  $M$ be an analytic connected 2-manifold with empty boundary, over the ground field
$M$ be an analytic connected 2-manifold with empty boundary, over the ground field  $\mathbb{F}=\mathbb{R}$ or
$\mathbb{F}=\mathbb{R}$ or  $\mathbb{C}$. Let
$\mathbb{C}$. Let  $Y$ and
$Y$ and  $X$ denote differentiable vector fields on
$X$ denote differentiable vector fields on  $M$. We say that
$M$. We say that  $Y$ tracks
$Y$ tracks  $X$ if
$X$ if  $[Y,X]=fX$ for some continuous function
$[Y,X]=fX$ for some continuous function  $f:\,M\rightarrow \mathbb{F}$. A subset
$f:\,M\rightarrow \mathbb{F}$. A subset  $K$ of the zero set
$K$ of the zero set  $\mathsf{Z}(X)$ is an essential block for
$\mathsf{Z}(X)$ is an essential block for  $X$ if it is non-empty, compact and open in
$X$ if it is non-empty, compact and open in  $\mathsf{Z}(X)$, and the Poincaré–Hopf index
$\mathsf{Z}(X)$, and the Poincaré–Hopf index  $\mathsf{i}_{K}(X)$ is non-zero. Let
$\mathsf{i}_{K}(X)$ is non-zero. Let  ${\mathcal{G}}$ be a finite-dimensional Lie algebra of analytic vector fields that tracks a non-trivial analytic vector field
${\mathcal{G}}$ be a finite-dimensional Lie algebra of analytic vector fields that tracks a non-trivial analytic vector field  $X$. Let
$X$. Let  $K\subset \mathsf{Z}(X)$ be an essential block. Assume that if
$K\subset \mathsf{Z}(X)$ be an essential block. Assume that if  $M$ is complex and
$M$ is complex and  $\mathsf{i}_{K}(X)$ is a positive even integer, no quotient of
$\mathsf{i}_{K}(X)$ is a positive even integer, no quotient of  ${\mathcal{G}}$ is isomorphic to
${\mathcal{G}}$ is isomorphic to  $\mathfrak{s}\mathfrak{l}(2,\mathbb{C})$. Then
$\mathfrak{s}\mathfrak{l}(2,\mathbb{C})$. Then  ${\mathcal{G}}$ has a zero in
${\mathcal{G}}$ has a zero in  $K$ (main result). As a consequence, if
$K$ (main result). As a consequence, if  $X$ and
$X$ and  $Y$ are analytic,
$Y$ are analytic,  $X$ is non-trivial, and
$X$ is non-trivial, and  $Y$ tracks
$Y$ tracks  $X$, then every essential component of
$X$, then every essential component of  $\mathsf{Z}(X)$ meets
$\mathsf{Z}(X)$ meets  $\mathsf{Z}(Y)$. Fixed-point theorems for certain types of transformation groups are proved. Several illustrative examples are given.
$\mathsf{Z}(Y)$. Fixed-point theorems for certain types of transformation groups are proved. Several illustrative examples are given.
 $Aff^{+}(\mathbb{R})$
                on compact surfaces with no fixed point: an elementary construction. Preprint, 2016, arXiv:1602.05736.Google Scholar
$Aff^{+}(\mathbb{R})$
                on compact surfaces with no fixed point: an elementary construction. Preprint, 2016, arXiv:1602.05736.Google Scholar