Table 3: Number of classes in observed works.

Task	Papers	Number
Classification, n=2 (binary classification)	[13, 18, 19, 20, 21, 23-26, 28, 29-34, 36, 38, 39, 41, 42]	21
Classification n=3	[27, 37, 40]	3
Classification n=5	[16, 43]	2
Classification n=6	[35]	1