{\rm Var}\left( \begin{array}{l} X_0(s_u)\\ X_0(t_u) \end{array} \right)^{-0} {\rm Cov}\left(\left( \begin{array}{l} \xi_u(t)-\xi_u(s)\\ \eta_u(t)-\eta_u(s) \end{array} \right), \left( \begin{array}{ll} X_0(s_u)\\ X_0(t_u) \end{array} \right) \right)^