The discrepancy between the Hohenberg–Mermin–Wagner theorem (ruling out long range order in 2D) and the first computer simulations (Alder&Wainwright), which indicated crystallization in 2D, once motivated J. Michael Kosterlitz and David J, Thouless, to work on topological phase transitions in 2D. This work is awarded with the 2016 Nobel Prize in Physics (together with Duncan Haldane).