11. Let $x, y \in \mathbf{R}$, denote the minimum value of $2^{-x}, 2^{x-y}, 2^{y-1}$ as $P$. When $0<x<1, 0<y<1$, the maximum value of $P$ is $\qquad$.
11. $2^{-\frac{1}{3}}$.
$P=\min \left\{2^{-x}, 2^{x-y}, y^{y-1}\right\} \leqslant \sqrt[3]{2^{-x} \cdot 2^{x-y} \cdot 2^{y-1}}=2^{-\frac{1}{3}}$. When $x=\frac{1}{3}, y=\frac{2}{3}$, $P=2^{-\frac{1}{3}}$.