Finite group action lens space orbifold Heat equation composite domain Fuglede-Putnam theorem sequential compactness Sixteenth problem of Hilbert Kolmogorov System Sine sum TAGSS School 2021 Xiao conjecture Prym varieties Hyperkähler Mori cone dependency equilibria Vector bundles birational geometry Waring decompositions matrix multiplication complexity Free curves Symmetric matrices symmetric tensors Quadric fibration