diff --git a/Day_4/Tasks_day_4.jl b/Day_4/Tasks_day_4.jl
index 56d1792..92333dd 100644
--- a/Day_4/Tasks_day_4.jl
+++ b/Day_4/Tasks_day_4.jl
@@ -5,6 +5,61 @@ using Markdown
 using InteractiveUtils
 
 # ╔═╡ 95f0a7c8-b065-11ec-0bd4-a9be6aca0c47
+md"""
+# Workflow outside notebooks
+Create a project directory somewhere in your file system. Now, `cd` into this project directory and create a project environment. Add some packages to this environment.
+
+Now, create two Julia files in this directory:
+- `main.jl`
+- `sub.jl`
+
+Write a function in the `sub.jl` file. Include this code in the `main.jl` file using the following inside `main.jl`:
+
+	include("sub.jl")
+
+Now, define a new function in `main.jl` that uses the function from `sub.jl`. Use `Measurements.jl` for some error calculation in one of these functions.
+
+Run Julia with the `--project=.` argument.
+
+Include only the `main.jl` file. Now run the function defined in `main.jl`.
+"""
+
+# ╔═╡ c2bbace2-3585-4a40-b54f-d466dd735716
+md"""
+# Startup
+Create the file `~/.julia/config/startup.jl`. Add the following lines into this file:
+
+```julia
+using OhMyREPL
+using Revise
+```
+
+Make sure that the two packages are in your global environment.
+
+Now launch Julia and test the syntax highlighting provided by `OhMyREPL`.
+"""
+
+# ╔═╡ 53bbb6c2-b264-4892-8e18-af8a1a5d5c2d
+md"""
+# Multithreading
+Open the tasks notebook of the first course day. Copy your function for the task about the squaring difference.
+
+Now, calculate all squaring differences for $i \in [1, N]$ with $N = 1000$ and store the results in a vector.
+
+Do this calculation without and with multithreading. What is the difference?
+
+Can you optimize more? Do some benchmarking!
+
+Plot the "squaring difference" of `i` against `i`.
+
+Hints:
+- You might need to use `BigInt`!
+- Verify that `Threads.nthreads()` returns a number bigger than one.
+- You have to import needed packages.
+"""
+
+# ╔═╡ 98112d63-c9df-4f4d-b961-ad26c76dd118
+# Your code starts here
 
 
 # ╔═╡ 00000000-0000-0000-0000-000000000001
@@ -23,6 +78,9 @@ manifest_format = "2.0"
 """
 
 # ╔═╡ Cell order:
-# ╠═95f0a7c8-b065-11ec-0bd4-a9be6aca0c47
+# ╟─95f0a7c8-b065-11ec-0bd4-a9be6aca0c47
+# ╟─c2bbace2-3585-4a40-b54f-d466dd735716
+# ╟─53bbb6c2-b264-4892-8e18-af8a1a5d5c2d
+# ╠═98112d63-c9df-4f4d-b961-ad26c76dd118
 # ╟─00000000-0000-0000-0000-000000000001
 # ╟─00000000-0000-0000-0000-000000000002