// stack:    inserts and removes happen at the same end
// inslast:  stack's action happens at the end called "last", "tail" or "back"
// inselem:  inserts happen via an element-level operation and removes happen via the api-provided "last"/"tail"/"back"

#define BOP_INIT(lst, iters, insNo, item)   BFX_INSERT_LAST(B_UserItem, lst, (item))

#define BOP_INSERT(lst, iters, insNo, item) BFX_INSERT_AFTER(B_UserItem, lst, (item), iters[(insNo)-1])
#define BOP_REMOVE(lst, iters, remNo)       BFX_REMOVE_LAST(B_UserItem, lst)