Show that the plane field in \(\mathbb {R}^3\) spanned by the vector fields \[ X=\frac {\partial }{\partial x}+z\frac {\partial }{\partial y} \qquad \text {and}\qquad Y=\frac {\partial }{\partial z} \] is not integrable
on any nonempty open subset of \(\mathbb {R}^3\).