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I wonder if Morse Theory on pseudo-Hermitian manifold is developed. For example, I wonder if the following statement on pseudo-Hermitian manifold, which is corresponding to the Riemannian case, is true:

Suppose $f$ is a smooth real-valued non-degenerate function on a pseudo-Hermitian manifold $(M,\theta)$, $a < b$, $f^{−1}[a, b]$ is compact, and there are no critical values between $a$ and $b$ in the sense that for all $x\in f^{−1}[a, b]$, the subgradient of $f$ at $x$ is not zero. Then $M^a$ is diffeomorphic to $M^b$, and $M^b$ deformation retracts onto $M^a$, where $M^a=f^{-1}(-\infty,a]$.

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I'm not familiar with the terminology "pseudo-Hermitian manifold". Could you include a definition or a link to a definition? –  Ryan Budney Apr 26 '12 at 6:01
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up vote 3 down vote accepted

Checking the various definition of "pseudo-Hermitian manifolds" in on-line papers, it seems they are in particular Finsler manifolds (there is a norm on the $T_x M$, continuously depending on $x$ ). In this case, one may apply the usual Lusternik-Schnirel'man theory (see e.g. Lusternik-Schnirelman theory on Banach manifolds, Topology 5 (1966), 115–132, by Richard Palais). In particular, the quoted statement follows.

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