A partial split of a set $S$ containing $n$ taxa is denoted by $A \mid B$, where $A$ and $B$
are disjoint subsets of $S$. The partial split is actually a generalization of the notion
of split in that we do not require that $A \cup B$ be equal to $S$.
Partial splits are used to model partial characters, where $A$ and $B$ represent the taxa
possessing or not possessing the character, respectively, and where we do not possess a
conclusion for all remaining taxa
