I have finally typed up full proofs for Xena, for the first question of M1F sheet 1.
Here are the questions in traditional PDF format: Example Sheet 1.
Here’s a link to a live Lean session containing the Solutions to all parts of Question 1 of this sheet. Click around and see if you can make any sense of it!
If you’d rather look at the questions than see the answers, here is a link to a Lean version of Question 1 from this sheet.