A library to model relationships between two objects that are subclasses of
Ord.
Instead using a Map structure we use a two Maps that allows
fast searching either by the key element or the value element.
Each of Map is between an element and a set of values.
Thus careful coordination of operations is required.
This library lacks of extensive testing, formal testing or automated testing.
Also in comparison to Data.Set or Data.Map (which provide the underlying
infrastructure used) there are some missing methods.
An example of use is the include source file T02_Relacion.hs.