Decreasing Power: Sort by order from high to low.

Such as: powerup: the 4th power of y+the 2nd power of y+the 2nd power of y+the 3rd power of x.

Decreasing power: cubic of x+quadratic of x+quartic of x+quadratic of x+y+y.

Note: the three items related to y can be arranged at will, because they are the 0 th item of X.