title: Combine sequence with itself recursively, without duplicates
body: <p>This is hard to explain but easy to show. Not sure why I haven't figured it out myself, so I must be missing something in clojure that is obvious.</p>
  
  <p>I need to combine a vector with itself, into a vector, and I need to combine the first element with all the remaining elements, then the 2nd element, with all the remaining elements (3rd and after).</p>
  
  <p>As a short example:
  [1 2 3 4 5]</p>
  
  <p>I need a function to get:
  [[1 2] [1 3] [1 4] [1 5] [2 3] [2 4] [2 5] [3 4] [3 5]]</p>
  
  <p>If this looks like getting half the pairs for a large matrix, you are right. I only want to solve half the matrix minus the middle diagonal. This is the only part I need to be sequential(so I only solve half) and the rest I want to use the reducers library to parallelize the heavier math in the background.</p>
  
  <p>Thanks in advance!</p>