Previous and next node in the list containing all the nodes of one type. The node is not part of a graph, iff typePrev is null. If typePrev is null and typeNext is not null, this node has been retyped and typeNext points to the new node. These special cases are neccessary to handle the following situations: "delete node + return edge", "hom + delete + return", "hom + retype + return", "hom + retype + delete", "hom + retype + delete + return".

public LGSPNode lgspTypePrev