The word symplectic in mathematics was coined in the late 1930's by Weyl [142, p.165] who substituted the Latin root in complex by the corresponding Greek root in order to label the symplectic group (first studied be Abel). An English dictionary is likely to list symplectic as the name for a bone in a fish's head.2 The name lagrangian manifold was introduced by Maslov [93] in the 1960's, followed by lagrangian plane, etc., introduced by Arnold [2].14 Whitney Extension Theorem: Let M be a manifold and X a submanifold of M . Suppose that at each p ∈ X we are given a linear isomorphism Lp : TpM ≃ −→ TpM such that Lp| TpX = Id TpX and Lp depends smoothly on p. Then there exists an embedding h : N → M of some neighborhood N of X in M such that h| X = id X and dhp = Lp for all p ∈ X. A proof relies on a tubular neighborhood model.
Lagrangian Submanifolds
First Lagrangian SubmanifoldsLet (M, ω) be a symplectic manifold.Definition 2.1 A submanifold X of (M, ω) is lagrangian (respectively, isotropic and coisotropic) if, at each p ∈ X, the space T p X is a lagrangian (respectively, isotropic and coisotropic) subspace of (T p M, ω p ).65 Even if the action is not free, the orbit through p is a compact submanifold of M . In that