 Let \(\bV = \{X_1, X_2 ,\ldots ,X_n\}\) be a set of endogenous variables, and \(\bU = \{U_1, U_2 ,\ldots ,U_n\}\) a corresponding set of exogenous variables. Suppose that each endogenous variable \(X_i\) is a function of its parents in \(\bV\) together with \(U_i\), that is: