 Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2015/discrete-mathematics-continuous-mathematics-and-probability-resit/2/d/ii/solution

n

independent choices on the diagonal. For each of the

(2 n)

{a, b}

of distinct elements, either both ordered pairs are included or neither is. Thus there are

2^{n + (2 n)}

2^{n^{2}} - 2^{n + (2 n)} = 2^{n^{2}} - 2^{n (n + 1) /2} .

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