2020 Invariants Michaelmas Puzzle Challenge

Solutions should be submitted to puzzles@invariants.org.uk no later than 14:59 BST on the Sunday after they are posted. Please quote your name, your institution, the week, and the numbers of the problems attempted in the subject line, e.g. Septus Quizonacci – University of Oxford – Week 7 – Problems 1,2,3.