in  Figure 9,  Y is a collider on the path \(\{U, Y, W, V, X\}.\) Let \(\mathbf{X}, \mathbf{Y}\), and \(\mathbf{Z}\) be disjoint subsets of \(\mathbf{V}\). \(\mathbf{Z}\) d-separates \(\mathbf{X}\) and \(\mathbf{Y}\) just in case every path \((X_{1}, \dots, X_{k})\) from a variable in \(\mathbf{X}\) to a variable in \(\mathbf{Y}\) contains at least one variable \(X_{i}\) such that either: (i) \(X_{i}\) is a collider, and neither \(X_{i}\) nor any descendant of \(X_{i}\) is in \(\mathbf{Z}\); or (ii) \(X_{i}\) is not a collider, and \(X_{i}\) is in \(\mathbf{Z}\). In  Figure 9,  \(\{U, V\}\) d-separates \(\{Y\}\) and \(\{X\}\). The path \(\{Y, W, Z, X\}\) contains a collider at Z, and all other paths from Y to X include U or V as a non-collider.