Greater<T> is a function object. Specifically, it is an
Adaptable Binary Predicate, which means it is a function
object that tests the truth or falsehood of some condition.
If f is an object of class
greater<T> and x and y are objects of class T, then
f(x,y) returns true if x > y and false otherwise.
Sort a vector in descending order, rather than the default ascending order.