title: How to get possible combinations of elements by adding two elements from list
body: <p>If list is [4,3,2,5]</p>
  <p>so pairs will be (43, 25), (3, 245), (53, 24)</p>
  <p>As they are combination of pairs of every element of list</p>
  <p>My question is, How to get above pairs for general list of these pairs?</p>