Legal plastic yield is actually the correct expression of plastic, such as hexadecimal 0x0A and octal book 060. Decimal numbers, binary numbers, escape characters, character concessions and other expressions, and so on.

y=((x=3×y，x+ 1)，x- 1)； It is a comma operation, and the value of the whole bracket is the calculation result of the previous formula, that is, y=x- 1. But before the calculation, the result of x is based on the previous calculation result, and then y=x- 1 is realized.