Implementing lab 4

[MostafaKhaled2017]

Goal

• Solving lab 4

Changes

• All changes are described in the file submissions/lab4.md

Testing

• Verification steps are described in the file submissions/lab4.md

Checklist

• Title is a clear sentence (<= 70 chars)
• Commits are signed (git log --show-signature)
• submissions/labN.md updated