Whitehead graph feature-region conjecture

Let $F$ be a free group, and associate to each element of $F$ the feature vector of weights of its Whitehead Graph in the corresponding feature space. A region is a bounded subset of that space whose boundary can be described by a hypersurface. Whitehead graph feature-region conjecture. These feature vectors are separated into bounded regions, each of which can be bounded by a hypersurface and corresponds to a particular Nielsen automorphism, in the sense that all elements in the corresponding class can be reduced by that automorphism. The conjecture is explicitly described as vague and is proposed as a model for the behavior of non-minimal elements; the source provides experimental motivation but no proof or resolution.