  For large $n$, take a random $n \times n$ permutation matrix and its
associated discrete copula $X_n$. For $a, b = 0, 1, \ldots, n$, let
$y_n(\frac{a}{n},\frac{b}{n}) = \frac{1}{n} ( X_{a,b} - \frac{ab}{n} )$; define
$y_n: [0,1]^2 \to R$ by interpolating quadratically on squares of side
$\frac{1}{n}$. We prove a Donsker type central limit theorem: $\sqrt{n} y_n$
approaches a bridged Brownian sheet on the unit square.
