PK_ERROR_code_t    PK_EDGE_ask_shells
(
--- received arguments ---
PK_EDGE_t          edge,              --- an edge

--- returned arguments ---
int         *const n_shells,          --- number of shells (>= 1)
PK_SHELL_t **const shells             --- shells (optional)
)


This function returns the set of shells which contain the given edge.


The output array shells is optional. If it is set to NULL, the function
will only compute the number of shells containing the edge.