ALLOW_DUPLICATES is false if duplicate elements shall not be allowed in
the list. The implementation may verify this at runtime. */
extern gl_list_t gl_list_create_empty (gl_list_implementation_t implementation,
gl_listelement_equals_fn equals_fn,
gl_listelement_hashcode_fn hashcode_fn,
ALLOW_DUPLICATES is false if duplicate elements shall not be allowed in
the list. The implementation may verify this at runtime. */
extern gl_list_t gl_list_create_empty (gl_list_implementation_t implementation,
gl_listelement_equals_fn equals_fn,
gl_listelement_hashcode_fn hashcode_fn,