# cobordism

## Which homology 3-spheres bound homology 4-balls? ★★★★

Author(s): Ancient/folklore

\begin{problem} Is there a complete and computable set of invariants that can determine which (rational) homology $3$-spheres bound (rational) homology $4$-balls? % Enter your conjecture in LaTeX % You may change "conjecture" to "question" or "problem" if you prefer. \end{problem}

Keywords: cobordism; homology ball; homology sphere

## Slice-ribbon problem ★★★★

Author(s): Fox

\begin{conjecture} Given a knot in $S^3$ which is slice, is it a ribbon knot? % Enter your conjecture in LaTeX % You may change "conjecture" to "question" or "problem" if you prefer. \end{conjecture}