PK_ERROR_code_t PK_CURVE_ask_fin
(
--- received arguments ---
PK_CURVE_t      curve,              --- a curve

--- returned arguments ---
PK_FIN_t *const fin                 --- owning fin (possibly PK_ENTITY_null)
)


This function returns the fin to which the given curve is attached,
if there is one, otherwise PK_ENTITY_null.