feat(Machines): Single-Tape Nondeterministic Turing Machines (NTMs)#683
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fmontesi wants to merge 5 commits into
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feat(Machines): Single-Tape Nondeterministic Turing Machines (NTMs)#683fmontesi wants to merge 5 commits into
fmontesi wants to merge 5 commits into
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crei
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Jun 26, 2026
crei
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Jun 26, 2026
Shreyas4991
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Jun 26, 2026
| /-- The transition labels used by a single-tape Turing Machine. -/ | ||
| inductive TrLabel (Symbol : Type*) | ||
| /-- Read `x` from the tape. -/ | ||
| | read (x : Symbol) |
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Why does read need a parameter. Shouldn't read just return whatever symbol is on the thread?
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This codifies the transition where the machine needs to read the symbol x to change states according to its transition relation. It's the usual thing in textbooks on TMs and automata, as well as labelled transition systems with 'observable actions'.
| (otape : Option (Turing.BiTape Symbol)) (μ : TrLabel Symbol) : | ||
| Option (Turing.BiTape Symbol) := | ||
| match μ, otape with | ||
| | read x, some tape => if x = tape.head then some tape else none |
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Why is the tape an option type? We always operate on the tape don't we?
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Because I need to use this with List.foldl in the NTM defs, but if you have a better suggestion I'm happy to hear it.
crei
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TrLabeland the usual derived 'yields' relation (Red).