Let's say I have a list of strings:

```
a = ['a', 'a', 'b', 'c', 'c', 'c', 'd']

```

I want to make a list of items that appear at least twice in a row:

```
result = ['a', 'c']

```

I know I have to use a for loop, but I can't figure out how to target the items repeated in a row.
How can I do so?

EDIT: What if the same item repeats twice in a? Then the set function would be ineffective

```
a = ['a', 'b', 'a', 'a', 'c', 'a', 'a', 'a', 'd', 'd']
result = ['a', 'a', 'd']

```