Derivations are the bread and butter of functional programming. It is easy to fall into the trap of thinking it is a pointless academic exercise, which is the reason why a lot of people struggle with FP. Functional programs are not so much written, they're calculated. It is here that the true power of equational reasoning (i.e. being able to swap the left and right parts of an equation everywhere in the code) help us.
So, getting comfortable reading and doing derivations is a must for any FP practitioner.
Below are the ones we did in the previous sessions, plus a couple of exercises.