The *genus $g$ handlebodies* are building blocks of $3$-manifolds. They are constructed from $3$-ball $B^3$ by adding $g$-copies of $1$-handles $B^2 \times B^1$. Their boundaries are homeomorphic to the genus $g$ surface $\Sigma_g$.

It turns out that any closed orientable $3$-manifold $Y$ can be obtained by gluing together two handlebodies $H_1$ and $H_2$ (such a decomposition is called *Heegaard splitting*):

 - $Y= H_1 \cup H_2$,
 - $\partial H_1 = \partial H_2 = \Sigma_g$.

The basic examples of such $3$-manifolds are

 - $S^3$,
 - $S^1 \times S^2$,
 - $S^1 \times S^1 \times S^1$,
 - [Lens spaces][1] $L(p,q) = S^3 / \mathbb Z_p$,
 - [Brieskorn spheres][2] $\Sigma(p,q,r) = \{ x^p + y^q +z^r = 0 \} \cap S^5 \subset \mathbb C^3$.

There are many references for Heegaard splittings of the first four of these examples, for example chapter 1 of Saveliev's book: *Lectures on the Topology of 3-Manifolds*.

How about the Brieskorn spheres? Is there an easy way to think about their Heegaard splittings? How can we draw them? Is there any good reference for this?


  [1]: https://en.wikipedia.org/wiki/Lens_space
  [2]: https://en.wikipedia.org/wiki/Brieskorn_manifold