Folder Challenge (Part #1)

A folder system on a computer might look something like the picture below.

In this challenge, folder systems will be represented by dictionaries where the keys are folders X and the value at X is the list of subfolders of X. For example, the picture above becomes the dictionary.

{
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}

The inputs for this challenge will be:

• A dictionary representing a folder system.
• Two folders, X and Y.

Write a function that decides whether "X is inside Y" (in the illustration, this means that you can travel down from Y to X).

Examples

is_it_inside({
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}, "B",  "A") ➞ True

is_it_inside({
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}, "B",  "D") ➞ False

is_it_inside({
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}, "I",  "D") ➞ True

is_it_inside({
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}, "A", "K") ➞ False

is_it_inside({
  "A": ["B", "C", "D"],
  "B": ["E", "F"],
  "D": ["G", "H"],
  "G": ["I", "J"],
  "H": ["K"]
}, "D", "D") ➞ True

Notes

• All the examples above use the folder system in the illustration, but the tests will use other folder systems as well.
• For the purposes of this challenge, any folder is inside itself, as in the last example.
• This challenge has a part 2.