“…In studies [31,32,35,37,42,[45][46][47]51] and [10], the activation functions are assumed to be in the real number field and quaternion field, respectively. In studies [30,33,36,38,39,41,43,44,48,49,53] and [14][15][16][17][18][19][20][21][22]26,29,34], the activation functions are assumed to meet the Lipschitz condition in the real field and quaternion field, respectively. Table 2 summarizes the review of existing work.…”