trings—that is, d(x, y) := |{i : xi = 1}| − |{i : yi = 1}| . (The vertical bars here are a little confusing: the bars around |{i : xi = 1}| and |{i : yi = 1}| denote set cardinality, while the outer...

trings—that is, d(x, y) := |{i : xi = 1}| − |{i : yi = 1}| . (The vertical bars here are a little confusing: the bars around |{i : xi = 1}| and |{i : yi = 1}| denote set cardinality, while the outer vertical bars denote absolute value.) For example, d(01000, 10101) = |1 − 3| = 2 and d(01000, 10100) = |1 − 2| = 1 and d(01000, 10000) = |1 − 1| = 0 and d(11010, 01010) = |2 − 2| = 0. Is d a metric?