add lab 4

# Lab 4

We have 2 branches here in this upstream repo for this lab:

- lab3-solution-good

- lab3-solution-bad

They both change `labs/lab3*` files. Seems like 2 different people worked on

the same files. It's possible there will be merge conflicts.

Check out both branches locally so you can work with them:

```

$ git fetch upstream

$ git branch lab3-solution-bad upstream/lab3-solution-bad

$ git branch lab3-solution-good upstream/lab3-solution-good

```

Once you go from task 1 to task 2 or vice versa, make sure to reset your local branches:

```

$ git switch lab3-solution-bad

$ git reset --hard upstream/lab3-solution-bad

```

## Task 1

Switch to `lab3-solution-bad` and rebase against `lab3-solution-good`.

## Task 2

Use interactive rebase to clean up commit history of `lab3-solution-bad` (top 4 commits).