“…We show, in Lemma 2.5, that every nonzero compound-commuting additive map is rank-one nonincreasing, i.e., the map sends rank one matrices to matrices of rank less than or equal to one. By using the structural results of rank-one nonincreasing additive maps on the space of block triangular matrices in [3], symmetric matrices in [8,7], and Hermitian matrices in [9,10,11], respectively, we characterize compoundcommuting additive maps on the spaces of square matrices, triangular matrices and symmetric matrices over arbitrary fields, and on the space of Hermitian matrices over a field with proper involution. We will see in Theorem 2.8 that the classification of compound-commuting additive maps on triangular matrices is quite different and essentially more complicated than the corresponding theorems on spaces of square matrices, symmetric matrices, and Hermitian matrices.…”