feat(MultiTapeTM): compose machines using tape transformations - #874
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SamuelSchlesinger wants to merge 2 commits into
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feat(MultiTapeTM): compose machines using tape transformations#874SamuelSchlesinger wants to merge 2 commits into
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SamuelSchlesinger
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chenson2018 and
fmontesi
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September 5, 2026 21:30
This was referenced Sep 5, 2026
crei
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I haven't read all of this PR yet, but I'm a bit surprised that there is still so much code to it. Maybe the plumbing is not abstract enough or does not have enough lemmas?
| - `InputFromWorkTape` simulates the native input on a work tape, preserving boundary clamping. | ||
| - `Rewind` shares one controller between native-input and work-tape rewinding. Work-tape rewind | ||
| starts immediately after contiguous contents and finishes at their first cell, including when empty. | ||
| - `Composition` assembles output redirection, work-tape rewind, and input substitution with `seq` |
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I think it would be better to first explain what it does and then how it does it. It reads like we already know where this is going.
| /-- Composition returns the second machine's output on the first machine's result. | ||
| The first halting time must be minimal; the second may be padded. -/ | ||
| theorem comp_haltsWithOutput | ||
| {input out₀ out₁ : List Symbol} {u v : ℕ} |
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| {input out₀ out₁ : List Symbol} {u v : ℕ} | |
| {input out₀ out₁ : List Symbol} {t\0 t\1 : ℕ} |
| /-! | ||
| # Correctness of multi-tape composition | ||
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| `comp_haltsWithOutput` proves that the composite machine returns the second machine's output |
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This could also be a bit more stand-alone. What is "the composite machine"?
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Construct machine composition from output redirection, work-tape rewind, and input substitution using the sequential combinator. Prove that the composite halts with the second machine's output on the first machine's result.
Part 5/6 of the TM composition stack. Depends on #873. Next: #875.
Validation: strict build, import checks, full tests, and linters.
This PR was composed with Astra via Codex.