title: Are C++ concepts a form of existential type?
body: <p>I was looking at the definition of existential types on Wikipedia (<a href="http://en.wikipedia.org/wiki/Type_system#Existential_types" rel="nofollow">Existential_types</a>) and it feels similar in some way to concepts in C++ (particularly to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3351.pdf" rel="nofollow">concepts lite</a>).</p>
  
  <p>Are C++ concepts a form of existential type?</p>
  
  <p>If not, what are the differences between the two?</p>