pub unsafe extern "C" fn igraph_contract_vertices(
graph: *mut igraph_t,
mapping: *const igraph_vector_int_t,
vertex_comb: *const igraph_attribute_combination_t,
) -> igraph_error_tpub unsafe extern "C" fn igraph_contract_vertices(
graph: *mut igraph_t,
mapping: *const igraph_vector_int_t,
vertex_comb: *const igraph_attribute_combination_t,
) -> igraph_error_t