x³y³ - 1/2x²y + y² - 2x³y³ + 0.5x²y + y² + x³y³ - 2y² - 3
=(x³y³ - 2x³y + x³y³ )+(- 1/2x²y+ 0.5x²y)+(y²+ y² - 2y² )-3
=-3