title: Find the function (a-b) U (b-a) of two sets of differences from the intersection, and difference set
body: <p>I tried understand this problem and answer but I did not get it since the code starting from Union
  How is that work? I didn't get that what is the question asks for..</p>
  <pre><code>def union(a,b):
      c = []
      for i in a:                
          if i not in b:        
              c.append(i)        
      c = c + b                  
      c.sort()                 
      return c
  
  def intersection(a,b):
      c = []               
      for i in a:
          if i  in b:
              c.append(i)
      c.sort()
      return c
  
  def complement(a,b):
      c = a + []
      for i in b:   
          if i in a: 
              c.remove(i) 
      c.sort()
      return c
  
  def double_complement(a,b):
      c = union(a,b) 
      d = intersection(a,b)
      e = complement(c,d)
      e.sort()
      return e
  
  
  a = [1,3,5,7,9,2]
  b = [2,4,6,8,0,7]
  
  double_complement(a,b)
  </code></pre>