a neighbour to star $i$ with coordinates $(X_{P_{i}},Y_{P_{i}},Z_{P_{i}},\Delta V_{\parallel_{i}},\Delta V_{\bot_{i}})$ if $$(X_{P_{i}}-X_{P_{j}})^2 + (Y_{P_{i}}-Y_{P_{j}})^2 +(Z_{P_{i}}-Z_{P_{j}})^2 \leq {r_{lim}}^2,$$ and $$\frac{(\Delta V_{\parallel_{i}}-\Delta V_{\parallel_{j}})^2}{a^2} + \frac{(\Delta V_{\bot_{i}}-\Delta V_{\bot_{j}})^2}{b^2} \leq 1.$$ The free parameters $a,b$ and ${r_{lim}}$ can be specified according to the goal of the study. We chose an elliptical shape for the velocity condition since the error ellipses in the tangential velocity plane can be eccentric. Indeed, in the case of the Praesepe sub-sample, $\sigma_{V_{\parallel obs}}$ and $\sigma_{V_{\bot obs}}$ are quite different; the mean $\sigma_{V_{\parallel obs}}$ is 0.79 km s$^{-1}$, and the mean $\sigma_{V_{\bot obs}}$ is 0.12 km s$^{-1}$. Considering also an intrinsic velocity dispersion in the cluster and tails, we chose 1.2 km s$^{-1}$ as the semi-major axis $a$ of our selection ellipse and 0.5 km s$^{-1}$ as the semi-minor axis $b$. With these velocity conditions we found, on average, 1.6$\times 10^{-5}$ stars for each velocity ellipse and per 1 pc$^{-3}$. Further we chose r$_{lim}$ = 15 pc to get, on average, 0.2 stars per 5-D neighbourhood volume. Note that we can determine neighbourhood only for those stars, where the volumes specified for neighbourhood are fully contained in the subset given in Sec. \[CVspace\]. This holds for 54652 stars which we 