code: def merge(x, y):
      
      z = []
      i = 0
      j = 0
      while i < len(x) or j < len(y):
          if j == len(y) or i < len(x) and x[i] <= y[j]:  # priority on x
              z.append(x[i])
              i += 1
          else:
              z.append(y[j])
              j += 1
      return z
docs: Merge two ordered lists
  
      :param x:
      :param y: x,y are non decreasing ordered lists
      :returns: union of x and y in order
      :complexity: linear