have a second observed feature $\lambda(O)_2$. Assuming $\lambda(O)_1$ was already identified as $\lambda(T)_1$ and $\Delta \lambda_{0-2}$ does not contain another theoretical line, $\lambda(O)_2$ will be marked as [unknown]{}. Although this is a rare case, it can be mentioned as a caveat of the algorithm (which also happens with regular ID methods). In panel (d) a second theoretical line $\lambda(T)_2$ is now in the list of candidates for $\lambda(O)_2$. Assuming $\lambda(O)_1$ was already identified as $\lambda(T)_1$, the [trunk-1]{} will force to $\lambda(O)_2$ to be identified as $\lambda(T)_2$ and not as $\lambda(T)_1$, missing the “unlikely" possibility of $\lambda(O)_2$ being a second velocity-component of $\lambda(O)_1$, and by some unknown mechanism $\lambda(T)_2$ was remove from our line-of-sight. Although rare, this also has to be mentioned as a caveat of the method. In panel (e), we allow the possibility of $\lambda(O)_1$ to have a second velocity-component, if $\lambda(O)_1$ was already identified as $\lambda(T)_1$, and $\lambda(O)_2$ as $\lambda(T)_2$, then $\lambda(O)_3$ will be identified as $\lambda(T)_1$. And finally in panel (f), there will be two duplets velocity-components with $\lambda(O)_1$ and $\lambda(O)_3$ identified as $\lambda(T)_1$, and $\lambda(O)_2$ and $\lambda(O)_4$ identified as $\lambda(T)_2$.

Although not complete, the list of possible cases cover the situations given in the present work. 