title: Lee Hwa Chung theorem
text: # Lee Hwa Chung theorem
  
  The Lee Hwa Chung theorem is a theorem in symplectic topology.
  
  The statement is as follows. Let M be a symplectic manifold with symplectic form ω. Let $\alpha$ be a differential k-form on M which is invariant for all Hamiltonian vector fields. Then:
  
     * If k is odd, $\alpha =0.$
  
     * If k is even, $\alpha =c\times \omega ^{\wedge {\frac {k}{2}}}$, where $c\in \mathbb {R} .$
  