Sorting is very important in computer programs. Therefore, Guile comes with several sorting procedures built-in. As always, procedures with names ending in ! are side-effecting, that means that they may modify their parameters in order to produce their results. The first group of procedures can be used to merge two lists (which must be already sorted on their own) and produce sorted lists containing all elements of the input lists. The following procedures can operate on sequences which are either vectors or list. According to the given arguments, they return sorted vectors or lists, respectively. The first of the following procedures determines whether a sequence is already sorted, the other sort a given sequence. The variants with names starting with stable- are special in that they maintain a special property of the input sequences: If two or more elements are the same according to the comparison predicate, they are left in the same order as they appeared in the input. Source.