The three Borromean rings. There are some properties of few-body systems that are “Universal”, so shared between all few-body systems that feel an attractive interaction (with certain boundary properties for defining eventual spin-orbit and isospin). An example of this behavior are the Efimov states of three-body systems: when an interaction loosely bound two bodies, the three-body system have a precise spectrum of excitation. This spectrum is observed in three nucleons systems like Helium-3 and Triton, since the two-body system, the deuteron, is loosely bound (for nuclear scales).