Curvature as infinitesimal holonomy

The equation hol$( - \nabla, \partial D) = \exp \ (- \int_{D} F)$ has an infinitesimal counterpart. If $X$ and $Y$ are two tangent vectors and we let $D_t$ be a parallelogram with sides $tX$ and $tY$ then the holonomy around $D_t$ can be expanded in powers of $t$ as

   hol$$\ (\nabla, D_{t}) = 1 + t^2 \ F (X, Y) + 0 (t^{3}).$$