This is maths:
(0 + 0)x = 0x
0x + 0x = 0x + 0
- 0x + (0x + 0x) = - 0x + (0x + 0)
(- 0x + 0x) + 0x = (- 0x + 0x) + 0
0 + 0x = 0 + 0
0x = 0
My professor told us at the beginning of last semester: Some people come in thinking they know everything about maths, and they're wrong; some other people come in thinking they know nothing about maths, and they're wrong too. I think, we didn't really know maths.
新年快乐!