func_code: def union(x, y):
      answer = []
      check = {}
      i = 0
      while i < len(x):
          if not x[i] in check:
              answer.append(x[i])
              check[x[i]] = True
          i = i + 1
      j = 0
      while i < len(y):
          if not y[j] in check:
              answer.append(y[j])
              check[y[j]] = True
          j = j + 1
      return check