Reindexing and composition theorem

FPRD-T106

Named finite controls can be reindexed without changing semantics

Exact statement

A named control-functional refinement with a supplied equivalence from its refined controls to a finite slot type can be reindexed and compiled without changing any input, hidden action, concrete stack, frontier, or accepting answer. Refinements compose, including at epsilon.

StatusMechanically checked and internally audited
External reviewNo documented external or specialist review of this FPRD result is recorded.

Context

The allocator uses slots indexed by Fin s, while mathematical machines usually use named states. Reindexing removes that syntactic mismatch without adding computational power.

Proof or evidence

Lean transports initialization, readout, and all three visible commands, proves exact frontier transport, refinement transitivity, control-functionality invariance, and compilation of both named and original machines.

Verification notes

The audit checked that only control names move: input letters, action tags, stack symbols, full stack contents, and round timing remain unchanged.

Limitations

  • A finite equivalence is supplied rather than synthesized from a generic Fintype instance.
  • Reindexing neither constructs the refinement nor supplies a new allocator beyond T104.

Open work

Package standard finite enumerations for common control carriers while retaining the supplied-equivalence boundary.

Notes

A core-only ControlEquiv supplies forward and inverse control maps with two inverse laws. Reindexing changes only control names: the initial control, final-control readout, and each successful call, return, or local target are transported, while the observed letter, hidden action, stack symbol, and entire concrete stack remain exact in the same input round. Lean checks the resulting T105 refinement, exact frontier transport, epsilon-aware acceptance, refinement transitivity including local completeness, and control-functionality equivalence. A named start/pushed/kept machine is an exact reindexing of the genuine fork and compiles both itself and the original non-control-functional merged source on all words. The theorem does not synthesize an equivalence from Fintype, add finiteness fields to the base machine, decide whether a finite refinement exists, or construct an allocator independently of T104. External alphabet finiteness, positive scaffold degree, reversal, and LMR remain outside Lean. This opens no M34 and does not edit the paused EPAL publication.