如何在列表列表中查找公共元素?

我想弄清楚如何比较 n 个列表以找到公共元素.例如:

I'm trying to figure out how to compare an n number of lists to find the common elements. For example:

p=[ [1,2,3],
    [1,9,9],
      ..
      ..
    [1,2,4]

>> print common(p)
>> [1]

现在，如果我知道元素的数量，我可以进行如下比较:

Now if I know the number of elements I can do comparions like:

for a in b:
  for c in d:
    for x in y:
...

但是如果我不知道 p 有多少个元素，那将不起作用.我看过这个比较两个列表的解决方案https://*.com/a/1388864/1320800

but that wont work if I don't know how many elements p has. I've looked at this solution that compares two lists https://*.com/a/1388864/1320800

但是在花了 4 个小时试图找出一种方法来实现递归之后，我仍然无法找到解决方案，因此非常感谢任何帮助！

but after spending 4 hrs trying to figure a way to make that recursive, a solution still eludes me so any help would be highly appreciated!