The factorial of a number in mathematics is the product of all the positive numbers less than or equal to a number.
But there are no positive values less than zero, so the data set cannot be arranged, which counts as the possible combination of how data can be arranged (it cannot).
In a group (G, *), the binary operation * is defined in such a way that the result of combining any two elements is always an element in the group. Therefore, if a, b ∈ G, then a * b ∈ G.