Exercise 5

This weeks exercise has been the most challenging!!!
I understand the proof structures but i find really challenging to come up with the in between part, specially when it seems so obvious or when we have to use precise definitions.
I found the first question to be really helpful to check basic understanding of proofs.
The second and third questions where a bit more challenging but i liked that it gave us the chance to disprove something in  the right format instead of just presenting a counter example.
What i have not been able to fully understand was question number 4