Support for linear homology (an emerging area in mathematics that involves geometry, topology and combinatorics).
These are used in the (candidate) formula for linear homology Betti numbers. Let W be a set containing a Fibonacci number of elements, such as the ways of writing some number n as a sum of a sequence of 1's and 2's. The formula for linear homology requires us, for each element w of W, to produce a subset sub(w) of W. These are the words w' in W that are subordinate to w.
This work will be developed in the fib-subset branch.