“…A complete classification of all possible soft theorems at various orders of the soft expansion has not appeared, although some discussion of it exists [79,80]. New soft theorems at various orders have recently been discovered in nonabelian gauge theories [20,77,81,82], supersymmetric theories [83][84][85], nonlinear sigma models [86], string theories [76,[87][88][89][90][91][92][93], and in other contexts [94][95][96][97][98]. Interesting universal structures are known for limits when two or more external particles are taken to be soft.…”