 Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2021/digital-systems-linear-algebra-introduction-to-formal-proof/5/b/ii/solution

E

interchanges rows three and four; applying it twice restores every row. Equivalently, it sends the standard basis vectors

e_{3}, e_{4}

to each other and fixes

e_{1}, e_{2}

, so its square fixes a basis. $E^{2} = I$ .

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