2 / 2 \ 3 / 3 \ 4 / 4 \
x*(y - y2) x *\y - 2*y2/ x *\y - 3*y2/ x *\y - 4*y2/
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y3 - y2 -2*y2 + 2*y3 -3*y2 + 3*y3 -4*y2 + 4*y3
$$\frac{x^{4} \left(y^{4} - 4 y_{2}\right)}{- 4 y_{2} + 4 y_{3}} + \frac{x^{3} \left(y^{3} - 3 y_{2}\right)}{- 3 y_{2} + 3 y_{3}} + \frac{x^{2} \left(y^{2} - 2 y_{2}\right)}{- 2 y_{2} + 2 y_{3}} + \frac{x \left(y - y_{2}\right)}{- y_{2} + y_{3}}$$
x*(y - y2)/(y3 - y2) + x^2*(y^2 - 2*y2)/(-2*y2 + 2*y3) + x^3*(y^3 - 3*y2)/(-3*y2 + 3*y3) + x^4*(y^4 - 4*y2)/(-4*y2 + 4*y3)