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> Theorem(Guillemin Sternberg Marle) Let $(M, \omega, \mu) $ be a symplectic manifold together with a Hamiltonian group action. Let $p$ be a point in $M$ such that $O\_p $ is contained in the zero level set of the moment map. Denote $G\_p$ the stabilizer and $O\_p$ the orbit of $p$. There is a $G$-equivariant symplectomorphism from a neighborhood of the zero section of the bundle $T^\*G ×\_{G\_p} V\_p$ equiped with a symplectic model to a neighborhood of the orbit $O\_p$.
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I'm looking for a reference of this theorem. ( The references that people recommend are the articles of Marle which is written in french and the article The normal form for the moment map by Guillemin and Sternberg which I can't download from internet). Could you please give some references where I can find the proof of this theorem.



Proof of the Hamiltonian slice theorem
The following textbooks contain a proof of the symplectic slice theorem:


* [Juan-Pablo Ortega and Tudor S. Ratiu: Momentum Maps and Hamiltonian Reduction](https://link.springer.com/book/10.1007/978-1-4757-3811-7)
* [Gerd Rudolph and Matthias Schmidt: Differential Geometry and Mathematical Physics](https://link.springer.com/book/10.1007/978-94-007-5345-7)


You might also have a look at my [PhD thesis](https://arxiv.org/abs/1909.00744). One of the main results is a symplectic slice theorem in infinite dimensions. Thus there also a lot of analytical questions that need to be answered, so maybe not the best point to start learning this topic.


