Suppose multiple iterator variables point to the node after the one being deleted. The the prev_ pointers become invalid pointers once the delete happens: nothing goes through the iterators fixing them. Thus they are invalidated. But sequence containers should only invalidate iterators pointing to the node being deleted and no others.

This mixes with the definition of iterator on page 264.

More normal would be to point back to the slist itself and to traverse to find the "prev" needed. more expensive the further down the list it goes but such leads to the correct set sof invalidated iterators.

I previously described how deleting Node N of a node based container is not supposed to invalidate the iterators pointing to node N+1 but that the slist example does. But I said "sequence container" where I should have said "node-based container". Sorry.

The slist::link_type* prev_ pointer usage can invalidate one or more iterators when erase deletes the node pointer to. Sequence containers are not supposed to invalidate any iterators referring the item following the erased one.