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In mathematics, the Conley conjecture, named after mathematician Charles Conley, is a conjecture in the field of symplectic geometry, a branch of differential geometry.

Let ${\displaystyle (M,\omega )}$ be a compact symplectic manifold. A vector field ${\displaystyle V}$ on ${\displaystyle M}$ is called a Hamiltonian vector field if the 1-form ${\displaystyle \omega (V,\cdot )}$ is exact (i.e., equals to the differential of a function ${\displaystyle H}$. A Hamiltonian diffeomorphism ${\displaystyle \phi :M\to M}$ is the integration of a 1-parameter family of Hamiltonian vector fields ${\displaystyle V_{t},t\in [0,1]}$.

In dynamical systems, one would like to understand the distribution of fixed points or periodic points. A periodic point of a Hamiltonian diffeomorphism ${\displaystyle \phi }$ (of period ${\displaystyle k}$) is a point ${\displaystyle x\in M}$ such that ${\displaystyle \phi ^{k}(x)=x}$. A feature of Hamiltonian dynamics is that Hamiltonian diffeomorphisms tend to have infinitely many periodic points. Conley first made such a conjecture for the case that ${\displaystyle M}$ is a torus.^[2]

The Conley conjecture is false in many simple cases. For example, a rotation of a round sphere ${\displaystyle S^{2}}$ by an angle equal to an irrational multiple of ${\displaystyle \pi }$, which is a Hamiltonian diffeomorphism, has only 2 geometrically different periodic points.^[1] On the other hand, it has been proved for various types of symplectic manifolds.

The Conley conjecture was proved by Franks and Handel for surfaces with positive genus.^[3] The case of higher dimensional torus was proved by Hingston.^[4] Hingston's proof inspired the proof of Ginzburg of the Conley conjecture for symplectically aspherical manifolds. Later, Ginzburg--Gurel and Hein proved the Conley conjecture for manifolds whose first Chern class vanishes on spherical classes. Finally, Ginzburg--Gurel proved the Conley conjecture for negatively monotone symplectic manifolds.