We say that 2 + 2 = 4, for instance, which is to say that each side is of equal sum. But it is less obvious that 4 = 2 + 2 insofar as 4 can also be the sum of 1 + 3. The point is that 2 + 2 can equal only one sum, 4; whereas 4 can be the sum of several combinations (2 and 2, 1 and 3, 10 and minus 6, and so on). And in this respect there is at least some asymmetry.
Amount. Asymmetric
