Like Bellavitis, Hamilton viewed vectors as representative of classes of equipollent directed segments. Subsequently the term vector was adopted for a class of equipollent line segments. Non-directed alternations are further subdivided into labile, equipollent, and suppletive alternations. The concept of equipollent line segments was advanced by Giusto Bellavitis in 1835. This act of a pope is denominated "equipollent" or "equivalent canonization" and "confirmation of "cultus"". The tangent vector to an affine geodesic is parallel and equipollent along itself. Two directed line segments are equipollent when they have the same length and direction.