2.1 Two-State Systems¶
https://www.youtube.com/watch?v=ZQW0cf059NA&list=PLMcpDl1Pr-vjXYLBoIULvlWGlcBNu8Fod&index=15
Some notes about permutations and combinations: https://www.youtube.com/watch?v=tEQFftB1Pao&list=PLMcpDl1Pr-vjXYLBoIULvlWGlcBNu8Fod&index=17