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[codex] DecidableEq と BEq の違いを説明#2347

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Seasawher merged 9 commits into
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codex/add-beq-page
May 26, 2026
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[codex] DecidableEq と BEq の違いを説明#2347
Seasawher merged 9 commits into
mainfrom
codex/add-beq-page

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Summary

Fixes #2005.

LeanByExample/TypeClass/Decidable.leanDecidableEqBEq の違いを説明する節を追加しました。

  • BEq が命題としての等号と一致しない例として、Accountid だけを見る比較を追加
  • LawfulBEq が必要になる場面を #synth の失敗例で確認
  • Float では BEq はあるが DecidableEq は合成できず、NaN == NaN が false になることを #guard で確認

Validation

  • lake env lean LeanByExample\TypeClass\Decidable.lean
  • lake build LeanByExample.TypeClass.Decidable

Note: local git could not create branches because .git/index.lock creation was denied, so this branch and commit were created through the GitHub connector.

@Seasawher Seasawher marked this pull request as ready for review May 26, 2026 17:08
@Seasawher Seasawher merged commit bda5211 into main May 26, 2026
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@Seasawher Seasawher deleted the codex/add-beq-page branch May 26, 2026 18:09
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DecidableEq と BEq の使い分け: BEqは Float のためにある

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