Canonical Noncommutative Defects Beyond Parikh Projection: Magnus Towers and an Unbounded Static-Dynamic Boundary Gap
We develop an order-sensitive defect formalism for substitution prefixes using the classical Magnus expansion of words. A substitution morphism induces a filtered endomorphism of the completed noncommutative tensor algebra, and an anchored substitution cut produces a multiplicative residual whose finite truncations form a compatible tower. The degree-one truncation recovers Parikh information, while higher degrees record scattered-subword data. For a finite substitution boundary language, we define the static separation depth $K_*$, the first Magnus depth at which every boundary word is distinguished, and for constant-length substitutions we define a dynamic stabilization depth $K_{\\mathrm{dyn}}$ by minimizing the corresponding depth-$k$ boundary-output automata. We prove: $$K_{\\mathrm{dyn}} \\le K_*$$ and give exact depth-two and depth-three models. The main result is an explicit primitive binary constant-length family $\\sigma_K$ such that: $$K_*(P_{\\sigma_K}) = K \\quad \\text{but} \\quad K_{\\mathrm{dyn}}(\\sigma_K) = 1 \\quad \\text{for every } K \\ge 2$$ Hence, the static order depth and dynamic defect depth can differ by an arbitrarily large amount. The proof explicitly separates classical input—Magnus expansions, $k$-binomial equivalence, Thue–Morse separation results, and automaton minimization—from the canonical substitution-boundary architecture and the resulting static-dynamic separation theorem.
Authors
- Tao Lin (ORCID: https://orcid.org/0009-0004-1291-515X)
Publication Details
- Journal
- Zenodo (CERN European Organization for Nuclear Research)
- Published
- 2026-09-14
- DOI
- https://doi.org/10.5281/zenodo.22759585
- Primary Topic
- semigroups and automata theory
- Type
- preprint