vb first = alloc (&_, T_LINK); detach (first, slice, REDUCE_SLICE);

vb first = alloc (&_, T_LINK); detach (first, &slice, REDUCE_SLICE);

vb first = alloc (&_, T_LINK); detach (first, slice, REDUCE_SLICE, ALLOW_EMPTY);

vb first = alloc (&_, T_LINK); detach (first, &slice, REDUCE_SLICE, ALLOW_EMPTY);