PK_ERROR_code_t    PK_POINT_ask_vertex
(
--- received arguments ---
PK_POINT_t         point,          --- a point

--- returned arguments ---
PK_VERTEX_t *const vertex          --- owning vertex (possibly PK_ENTITY_null)
)


This function returns the vertex connected to the given point, if there is one,
otherwise PK_ENTITY_null.