 To satisfy the triangle inequality, the sum of "any" two of these three sides must be greater than or equal to the remaining side.However, the distance between {a} and {a,b} plus the distance between {b} and {a,b} equals 2/3 and is therefore less than the distance between {a} and {b} which is 1.The Sørensen–Dice coefficient is useful for ecological community data (e.g.