new_contents: import sys
  
  edges = {}
  seen = {}
  offsets = {}
  max_vertex = 0
  s = open(sys.argv[2], "w+")
  with open(sys.argv[1]) as f:
      for line in f:
          arr = line.split("\t")
          u = int(arr[0])
          v = int(arr[1])
          seen[u] = True
          seen[v] = True
          if u not in edges:
              edges[u] = {}
          if v not in edges:
              edges[v] = {}
          edges[u][v] = True
          edges[v][u] = True
          if max_vertex < u:
              max_vertex = u
          if max_vertex < v:
              max_vertex = v
  
  offset = 0
  for u in range(max_vertex + 1):
      if u in seen:
          offsets[u] = offset
      else:
          offset += 1
  
  for u in sorted(edges.keys()):
      for v in sorted(edges[u].keys()):
          if u != v and u in edges and v in edges[u] and u < v:
              s.write(str(u - offsets[u] + 1) + "\t" + str(v - offsets[v] + 1) + "\n")
  
subject: add web network cleaner