Simplify the expression 2 - (y3)/(x4)(y4-y3)/(x4)

The complex fraction is $\frac{\frac{y^3}{x^4}}{\frac{y^4-y^3}{x^4}}$.
To simplify, multiply the numerator by the reciprocal of the denominator:

$$\frac{y^3}{x^4} \cdot \frac{x^4}{y^4-y^3}$$

Cancel out the $x^4$ terms:

$$= \frac{y^3}{y^4-y^3}$$

Factor out $y^3$ from the denominator:

$$= \frac{y^3}{y^3(y-1)}$$

Cancel out $y^3$ (assuming $y \neq 0$):

$$= \frac{1}{y-1}$$

The expression becomes:

$$2 - \frac{1}{y-1}$$

To do this, find a common denominator, which is $(y-1)$:

$$= \frac{2(y-1)}{y-1} - \frac{1}{y-1}$$

Combine the numerators:

$$= \frac{2(y-1) - 1}{y-1}$$

Distribute the 2 in the numerator and simplify:

$$= \frac{2y - 2 - 1}{y-1}$$ $$= \frac{2y - 3}{y-1}$$

The simplified expression is $\frac{2y-3}{y-1}$.