A set is a mathematical term used for a loose collection of objects, called elements.
They are often represented by brackets enclosing their elements (e.g., {1,4,−13.5}).
In contrast to permutations, the order of the elements in a set is not important, so that
{1,4,−13.5} is the same set as {−13.5,1,4}. Also, the elements of a set are not
allowed to repeat (as is the case for multisets), so that {−1,2.5,−1,0} does not represent a
well-defined set.