The Interval class doesn’t have an attribute to store that the plus/minus was specified for the interval. Is this inferred in some other way or should a “plus_minus” attribute be added to the Interval class?
Then the “lower” would be “N” and “upper” would be “M”.
An interval of N ±M can be transformed into lower…upper but the original format (and intention of the modeler) is lost.
For the understanding of the constraint it is not the same to display it as “56…64” instead of “60 ±4”.