Category:Wren-maputil
This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.
Wren-maputil is a module which supplements the methods in the Wren programming language's Map class. It consists of two classes: MapUtil and MultiSet all of whose methods are static.
It is the thirty-seventh in a series of modules (listed on the language's main page) designed to assist with writing Rosetta Code tasks so the same code does not have to be written or copy/pasted time and time again thereby bloating a task's script code unnecessarily.
To use it all you need to do is to copy the source code (in the talk page) to a text file called maputil.wren and place this in the same directory as the importing script so the command line interpreter can find it.
As there is a dependency on the Wren-check module, you also need to copy that (if it is not already present) to the same directory as described here.