PK_ERROR_code_t PK_FACE_euler_unslit
(
--- received arguments ---
PK_FACE_t       face,       --- Face to be unslit
PK_EDGE_t       surviving   --- Edge to survive the unslit
)


This function replaces a 2-edge face with an edge.


Specific Errors:
    PK_ERROR_invalid_face         wrong number of loops or edges on face
    PK_ERROR_bad_edge             surviving not on face
    PK_ERROR_edge_not_manifold    surviving is not manifold or the other
                                  edge is neither manifold nor laminar


This function deletes a slit face.  The given face must have either one loop
and two edges or two loops each with one ring edge.

surviving must be manifold and the other edge of the face must be either
manifold or laminar.  The edges need not have the same direction.

The surviving edge will be retained and the other edge will be deleted.

If face or the edge to be deleted have geometry attached then this will be
deleted.  The resulting body will normally be invalid.

The inverse to this function is PK_EDGE_euler_slit.