Kicked calc 2’s butt

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Need help in understanding this congruence relation

Abstract algebra is the subreddit for all things related to modern, university and research level algebra.
Let some friends use my 5x5, never doing so again 😐

For people who love any sort of twisty puzzles, including but not limited to: Rubik's Cubes (and any size/design variants), the Square 1, the Pyraminx and more.