Prefix Min Operation

Some problems require "prefix min": replace $f(x)$ with $\min_{y \leq x} f(y)$. This truncates the function, keeping only the minimum value for all $y$ up to $x$.

In heap terms: after computing $f(x)$ for all $x$, you want the function to be non-increasing. Pop from the min-heap until it's empty, leaving only the max-heap. This operation changes the function shape but preserves the slope-change representation. Use it when constraints force monotonicity.