Add proofs on truth value#2418
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(I've simplified the proofs, but the statements remain unchanged) |
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Other than the one name choice, this is great.
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Adds a handful of properties that prove the truth
value of a decidable:
- `Relation.Nullary.Decidable`:
- `does-≡`: decidables over the same type have the same truth value
- `does-⇔`: generalization of `does-≡` to mutually implied types
- `Relation.Unary.Properties`:
- `≐?`: generalization of `Decidable.map` to predicates
(if two predicates are equivalent, one is decidable if the other is)
- `does-≡`: generalization of `does-≡` to predicates
- `does-≐`: generalization of `does-⇔` to predicates
Co-authored-by: jamesmckinna <31931406+jamesmckinna@users.noreply.github.com>
Co-authored-by: jamesmckinna <31931406+jamesmckinna@users.noreply.github.com>
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@JacquesCarette are you willing to approve now? |
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| does-≡ : (a? b? : Dec A) → does a? ≡ does b? | ||
| ``` | ||
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| * In `Relation.Nullary.Properties`: |
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We missed this (copy/paste error?) during review: should be Relation.Unary.Properties!
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Nice spot! Any chance of a quick PR?
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Adds a handful of "congruence" proofs on the truth value of a decidable, and also
≐?:Relation.Nullary.Decidable:does-≡: decidables over the same type have the same truth valuedoes-⇔: generalization ofdoes-≡to mutually implied typesRelation.Unary.Properties:≐?: generalization ofDecidable.mapto predicates (if two predicates are equivalent, one is decidable if the other is)does-≡: generalization ofdoes-≡to predicatesdoes-≐: generalization ofdoes-⇔to predicatesUsing these, together with the definitions in
Decidable.Core, one can prove the effect of type operations on truth value. For example, proving thatDec (¬ A)andDec Ahave negated truth values can be done asdoes-≡ ¬a? (¬? a?). Same with×/∧and⊎/∨.