map_val_t sl_lookup (skiplist_t *sl, map_key_t key);
map_val_t sl_remove (skiplist_t *sl, map_key_t key);
size_t sl_count (skiplist_t *sl);
map_val_t sl_lookup (skiplist_t *sl, map_key_t key);
map_val_t sl_remove (skiplist_t *sl, map_key_t key);
size_t sl_count (skiplist_t *sl);