What is different about mathematical sets and STL sets?

What will be an ideal response?

In mathematics, sets have no structure. The elements are not in order, all
you can tell about a set is whether it is empty and count the members. I perhaps need
to say some weasel words here about some mathematical niceties, but I refrain. You
can tell whether a given candidate is a member of a mathematical set. The STL set
supports all the tests on a mathematical set can be performed on an STL set. On the
other hand, the elements of the STL set are kept sorted. There is a first and a last
element. You can tell whether an STL set is empty and determine the size. These seem to be the most important differences and similarities.