The concrete derived AssocPersSubentId class that identifies an edge subentity if the entity has only a single edge subentity (such as in the case of curve entities).

Autodesk.AutoCAD.DatabaseServices.AssocPersSubentityId
    Autodesk.AutoCAD.DatabaseServices.AssocSingleEdgePersSubentId

Public Class AssocSingleEdgePersSubentId
Inherits AssocPersSubentityId

public class AssocSingleEdgePersSubentId : AssocPersSubentityId;