= Solution
Since $H_0$ and $f_0$ depend only on the <action variables>, $\{f_0,H_0\}=0$. Drop the quadratic term $\{\delta f,\delta\Phi^{\mathrm{tot}}\}$ from the <Vlasov equation> in <3/a>. Defining the orbital <frequency> vector by $\boldsymbol\Omega(\mathbf J)=\partial H_0/\partial\mathbf J$, the linearized equation is
$$
\boxed{\partial_t\delta f+\boldsymbol\Omega\cdot\partial_{\boldsymbol\theta}\delta f-\frac{\partial f_0}{\partial\mathbf J}\cdot\partial_{\boldsymbol\theta}\delta\Phi^{\mathrm{tot}}=0.}
$$
The sign of the driving term follows from the second term in the canonical <Poisson bracket>, because the background has no angle dependence.
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