_prop_number
typedef struct _prop_number *prop_number_t;
const struct _prop_number *pn1 = n1;
const struct _prop_number *pn2 = n2;
const struct _prop_number *pn = n;
.rbto_node_offset = offsetof(struct _prop_number, pn_link),
_PROP_POOL_INIT(_prop_number_pool, sizeof(struct _prop_number), "propnmbr")