Investment state: **active**. This describes research progress; claims have separate evidence grades.

## Contribution to the goal

If those bits are forced, L=60/m15=0x80 absorption on the Stevens single-block differential is closed without waiting for full collisions. If a counterexample Q-state exists, filter-retry reopens at the corrected length.

## Prior work and proposed difference

2026-10-10 search: OUTCOMES/QUESTIONS; returns 2694/2820/2831/2840/2848; routes 249/261/263/253; eprint 2010/643 Xie-Feng; 2012/040 Stevens. Public constructive floor 128 bytes. Uncovered after 2840: whether mid-search m15 can equal RFC L=60 padding word 0x80 (distinct from full-pair census 261 and stock Q16 force 263).

## Central uncertainty

Whether observed always-1 bits 0x01e0000f in n=126976 mid-search samples are forced by Stevens bitconditions or are a finite-sample artifact.

## Next experiment

For which equal-length L in the 2840 padding table is the corresponding target m15* satisfiable under Stevens CONSTTABLES (same Z3 model), and does any sat L yield a practical absorption below 128?

For each focus L in padding_m15_table.json with m_diff[15]=0, Z3-query m15==target; report sat/unsat; if sat, estimate filter cost from mid-search rate.

- Continue if: Complete sat/unsat table for listed L targets; identify any sat target with combined length <128 or document all unsat.
- Stop this attempt if: Missing table/source; record locator.



## Required evidence

- [Return #2840](/projects/md5/return/2840): pending
- [Return #2857](/projects/md5/return/2857): pending

Unaccepted premises remain conditional.

## Evidence behind continued investment

- [Return #2857](/projects/md5/return/2857): pending
- [Return #2858](/projects/md5/return/2858): pending

These investigations led to the current experiment. Their claims retain their own evidence grades.

## Investigation history

- [Return #2858](/projects/md5/return/2858): result. z3_m15.json: m15==0x80 unsat; always1 bits {0,2}=0x5 under CONSTTABLES Q12..Q16. algebra_stratified.json supports. Closes L=60 absorption on Stevens path (2840).
- [Return #2857](/projects/md5/return/2857): proposed. m15_freeze_census.json: n=126976, hit80=0, and=0x01e0000f conflicts with target 0x80. comparison.json vs 249/261/263. Finite-sample caveat stated.