refactor(MultiTapeTM): Put the output tape into the configuration - #818
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refactor(MultiTapeTM): Put the output tape into the configuration#818barni120400 wants to merge 1 commit into
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The configuration gains an `output` field holding the symbols emitted so far, `step` appends to it and `initCfg` starts it empty. The output of a run can then be read off its final configuration, so `outputString` and its lemmas are replaced by `step_output` and existing facts about `configs`, and `ComputesInTimeAndSpace` reads the output from the configuration it already mentions. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Superseded by #819, which contains this change plus a rename of |
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The output tape is now part of the configuration:
Cfggains anoutputfield,stepappends the symbol the transition emits, andinitCfgstarts it empty. The output of a run is then whatever is on its final configuration's tape.That makes
outputStringunnecessary, so it and its lemmas are removed.outputString_succbecomesstep_output,outputString_eq_of_haltis restated on configurations, andoutputString_haltandoutputString_add_eq_appendwere output-flavoured restatements of the existingconfigs_of_haltsandconfigs_add.ComputesInTimeAndSpacenow reads the output off the configuration it already mentions. Net -30 lines, no change in meaning.This is step 1 of the plan discussed on Zulip: with the output in the configuration, a
Listof configurations determines the output string, so a computation can be such a list and reuse the machinery inRelatesInSteps.lean.Note that the configuration space is now unbounded, so counting reachable configurations needs to happen on the storage configuration rather than on
Cfg.NB: claude was used heavily throughout.