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160 • Chapter 5: Evaluation and Simplification> simplify( expr, {siderel}, [x,y] );y 3 − x y 2 + x> simplify( expr, {siderel}, [y,x] );x 3 − y x 2 + yIn the first case, Maple makes the substitution x 2 = 1 − y 2 in theexpression, then attempts to make substitutions for y 2 terms. Not findingany, it stops.In the second case, Maple makes the substitution y 2 = 1 − x 2 in theexpression, then attempts to make substitutions for x 2 terms. Not findingany, it stops.Gröbner basis manipulations of polynomials are the basis of howsimplify works. For more information, refer to ?simplify,siderels.Sorting Algebraic ExpressionsMaple prints the terms of a polynomial in the order the polynomial wasfirst created. You may want to sort the polynomial by decreasing degree.The sort command makes this possible.> poly := 1 + x^4 - x^2 + x + x^3;poly := 1 + x 4 − x 2 + x + x 3> sort( poly );x 4 + x 3 − x 2 + x + 1Note that sort reorders algebraic expressions in place, replacing theoriginal polynomial with the sorted copy.> poly;x 4 + x 3 − x 2 + x + 1You can sort multivariate polynomials in two ways, by total degree orby lexicographic order. The default case is total degree, which sorts termsinto descending order of degree. With this sort, if two terms have the