Note that the argument, the list to be sorted, is pattern matched as (p:xs) which means that p is the first element of the list, and xs is the rest of the

Note that the argument, the list to be sorted, is pattern matched as (p:xs) which means that p is the first element of the list, and xs is the rest of the elements (i.e., xs does not contain p). In the definition of "greater": greater = filter (>= p) xs , the filter is applied to xs, which means that p will not be included.