Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2023/iii/paper-160/3/a/i/solution

Use a beta set on an -runner partition abacus. A hook of length divisible by corresponds to a bead and a gap on the same runner. Divide both runner positions by . They become a bead and a gap at distance in the runner partition , and hence determine a hook there. This gives the required bijection, with .
Removing replaces the bead by the gap . On its runner this is exactly the bead move that removes , while every other runner is unchanged. Thus hook removal commutes with the construction and
This is the abacus divisible-hook correspondence.

New to topics? Read the docs here!