The first is all the values of x, which can be any number; The second is all values of y, and y must be greater than or equal to 0;

The third is all points on the curve y = x 2; The fourth says that y = x 2 is a subset of it.

The first meaning is that its subset is the value of x, that is, {- 1,-197, ... 1, 2, 3, ...} X can take any number.

The second means that its subset is the value of y, that is, {0, 1, 2, ...) Because y = x 2 and x 2 is greater than or equal to 0, y must also be greater than or equal to 0.

The third means that its subset is all points on the curve, namely {(0,0), (1, 1), (2,4) ...}

The fourth is that this equation is a subset of this set, that's all.