[seafoamteal]

Hi! Yes, I talk about this a little bit at the end and I solve Part 2 the normal way. This is a toy example that I did for fun. The objective was to introduce people to Program Construction and show how you can use formal methods to derive correct programs. Whether the juice is worth the squeeze is a judgement call that you make depending on how critical the software you are writing is.

[Joker_vD]

But the resulting algorithm is just... weird. It operates under the assumption that the elements f.i can be arbitrary e.g. negative or greater than 9 — which they can't. And adopting that assumption allows you to dispense with keeping track of the variations of the total sum and merely track the separate digits themselves, which would allow a non-mechanical programmer to see easily that the algorithm is correct.