Propriety, stability, and co-stability

Lumma stability may be computed by taking all the overlaps between
intervals, adding them up, dividing by the number of scale degrees,
and subtracting that from 1. If the highest value of class(i) minus
the lowest value of class(i-1) is positive, then you add it,
otherwise, not.

We can then define Lumma propriety as what you get by adding only if the
highest value is *less* than the lowest value, instead of greater.
Change sign, and don't subtract from 1, and you have Lumma propriety.
In other words, Lumma propriety is co-Lumma stability, so I withdraw
my objection, and will call what you get by adding up the lenghts of
intervals by some other name.