C++0x issue: Constant time insertion into std::set

Question

According to this page, I can achieve constant time insertion if I use

iterator std::set::insert ( iterator position, const value_type& x );

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Answer 1

Only supplying an iterator that falls immediately after the new value makes any sense.

That's because in a collection of N elements, there are N+1 possible insertion points. An iterator exists that comes after a value higher than any preexisting element, but there is no iterator that comes before a value before all elements.