Creating hyperbolic-regular singularities in the presence of an ${\mathbb{S}}^1$-symmetry

On a 4-dimensional compact symplectic manifold, we study how suitable perturbations of a toric system to a family of completely integrable systems with ${\mathbb{S}}^1$-symmetry lead to various hyperbolic-regular singularities. We compute and visualise associated phenomena like flaps, swallowtails, and $k$-stacked tori for $k\in \{2,3,4\}$ and give an upper bound for $k$ in our family of systems.