“…The four-body problem. Although unsolved problems remain, for the Newtonian (A = 3) and vortex case (A = 2) of the four-body problem the central configurations are well understood, with many particular results for configurations with some special symmetry or other properties [77,39,86,49,15,104,54,84,55,61,75,108,9,62,110,128,35,143,11,18,63,43,37,46,30,122]. The equal mass case is especially well characterized.…”