26.5 `self`, **14.2**, 14.3 selection sort, **19.3**, 19.6 Selenium, 24.5 semantic versioning, **23.3** sentinel value, **5.5**, 5.6 set, **9.5**, 9.6 `add()`, **9.5** `difference()` / `-`, **9.5** `discard()`, **9.5** `intersection()` / `&`, **9.5** `remove()`, **9.5** `symmetric_difference()` / `^