public Concept lowestCommonAncestor(String v, String w) {
        Concept vnode = getConcept(v);
        Concept wnode = getConcept(w);

        return lowestCommonAncestor(vnode, wnode);
    }
public Concept lowestCommonAncestor ( String v , String w ) { Concept vnode = getConcept ( v ) ; Concept wnode = getConcept ( w ) ; return lowestCommonAncestor ( vnode , wnode ) ; }
Returns the lowest common ancestor (LCA) of concepts v and w. The lowest
common ancestor is defined between two nodes v and w as the lowest node
that has both v and w as descendants (where we allow a node to be a
descendant of itself).