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(a-3)*(a+5)-(2*a-5)=a^2-10
2*x*y^2-18*x=2*x*(y-3)*(y+3)
(b-1)^2*(b+2)-b^2*(b-3)+3=3*b^2-3*b+5
x+y-x^3-y^3=-(y+x)*(y^2-x*y+x^2-1)
