be the pseudohermitian volume form, let $R_\theta\in C^\infty(M;\mathbb R)$ be the Webster scalar curvature, let $\nabla_b$ be the horizontal gradient, and let $\Delta_b:C^\infty(M;\mathbb R)\to C^\infty(M;\mathbb R)$ be the sub-Laplacian with the sign convention
for all $f,g\in C^\infty(M;\mathbb R)$. Assume the Webster scalar curvature is normalized so that, for every positive $w\in C^\infty(M;\mathbb R)$ and $\widetilde\theta:=w^{2/n}\theta$, the conformal transformation law is
Suppose $u\in C^\infty(M;\mathbb R)$ satisfies $u>0$ on $M$ and is a critical point of $Q_\theta$ with respect to all smooth real variations, meaning that for every $\varphi\in C^\infty(M;\mathbb R)$ the derivative
exists and is equal to $0$, where $s$ is restricted to sufficiently small real values so that $u+s\varphi>0$ on $M$. Then there exists $\lambda\in\mathbb R$ such that