Local Weierstrass preparation I could not find a reference of the local version of Weierstrass preparation theorem It is used for example in Denef &amp; van den Dries "$p$-adic and real subanalytic sets".
Can you help, thank you
See '$p$-adic numbers, $p$-adic analysis, and zeta-functions' by Koblitz. Chapter IV sections 3 and 4 have a good exposition on newton polygons and the Weierstrass preparation theorem.
A good elementary proof of the Weierstrass preparation theorem can be found in the Jun-ichi Igusa's An introduction to the theory of Local Zeta Functions (Google books link).

See Chapter 2, section 2.3.