We link the structure of nuclei around 100Sn, the heaviest doubly magic
nucleus with equal neutron and proton numbers (N=Z=50), to nucleon-nucleon
(NN) and three-nucleon (NNN) forces constrained by data of few-nucleon
systems. Our results indicate that 100Sn is doubly magic, and we predict
its quadrupole collectivity. We present precise computations of 101Sn
based on three-particle--two-hole excitations of 100Sn, and reproduce the
small splitting between the lowest Jπ=7/2+ and 5/2+ states. Our
results are consistent with the sparse available data.Comment: 8 pages, 4 figure