Questions tagged [agda]

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"Universe-shrinking" function in Agda

Agda does not allow datatypes in one universe to be indexed by, or non-trivially parametrized by a type in a larger universe (strangely, Coq does not appear to require this for propositional ...
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1answer
57 views

Proving intuitionistic tautologies in Agda

I am to use Agda to prove some intuitionistic tautologies. One of them is the so called Weak Peirce's Law $$ ((((A \rightarrow B) \rightarrow A) \rightarrow A) \rightarrow B) \rightarrow B $$ I ...
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Are Agda's inductive-inductive types safe?

An inductive-inductive definition is a kind of simultaneous inductive definition of a type $A : \mathcal U$ and a type $B : A \to \mathcal U$. I think Agda also lets you extend this idea in all of ...
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1answer
103 views

Which would be better for programming using Homotopy type theory Agda or Idris

I'm looking to model data inputs for an artificially intelligent system, which is affected by its internal parts and has feedback loops. I'd like to model it mathematically, using category theory or ...
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1answer
47 views

Why does universe level restriction behave differently between inductive family and parameterized inductive type without axiom K in agda

An observation when defining List in agda with --without-K enabled: The following parameterized inductive definition is accepted:...
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1answer
304 views

Relationship between inductive families and type-returning functions

Dependently typed languages such as Agda support inductive families, also called indexed datatypes, which allow type parameters to vary between constructors. This can be used to define a set of ...
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2answers
86 views

Interpreting a proof of $2^\mathbb{N}$ being uncountable

Suppose I have the following proof: ...
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0answers
76 views

Does Type:Type lead to inconsistency without general inductive types?

In e.g. Agda , it is possible to derive an element of the empty type by enabling the "type in type" option. Every proof I have seen (and come up with) involves making a special inductive type ...
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1answer
69 views

Which inductive schemes can encode the following Agda definition?

Which induction schemes (e.g. induction-recursion by Dybjer and Setzer, "Irish" induction-recursion by McBride or induction-induction by Forsberg and Setzer or perhaps some simpler ones) allow one to ...
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0answers
113 views

Predecessor function with recursive types

I am defining the type Nat of natural numbers a recursive sum type: $$ Nat = \mu X. Unit \oplus X$$ Now, I have defined zero ...
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1answer
145 views

Is this statement of P = NP in Agda correct?

Looking for a self-contained statement of P = NP in type theory, I stumbled upon this short Agda formalization (a cleaned up version is reproduced below). The statement here does seem to express the ...
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2answers
105 views

Propositional truncation of excluded middle

It is clear to me that it should be impossible to prove : exclMidl = isProp A → ((A) ⊎ (¬ A)) Because it would give deciding oracle for every Proposition. My ...
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0answers
134 views

Strict Positivity of Indexed Datatype in Agda

Agda is ruling out definitions like data Bad : Set where bad : (Bad → Bad) → Bad Because "Non strictly-positive declarations are rejected because one can write ...
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1answer
292 views

Proof that type does not have decidable equality in Agda

Can one create such function in Agda ? ℕ→ℕ-undecidable : ¬ ( (f g : ℕ → ℕ ) → Dec (f ≡ g)) ℕ→ℕ-undecidable = ? I am particularly interested in proof using ...
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1answer
153 views

Can one get Turing-completeness without nontermination?

As I'm reading the movfuscator paper by Stephen Dolan, I encounter this claim: In order to have Turing-completeness, we must allow for nontermination. This seems like a reasonable statement. But I'...
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1answer
257 views

Why this pattern matching fails in Agda?

Consider function wa'' (need natural number definition, either in stdlib or Agda.Builtin.Nat): ...
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2answers
390 views

In Agda's GADT, are "parameterized" and "indexed" different semantically?

I know they have different scoping: data a (n : Set) : Set where introA : a n data b : Set -> Set where introB : {n : Set} -> b n That's not what I'...
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1answer
300 views

What does it mean if we disable K-rule in Agda?

TL;DR: Can I say, "K-rule in Agda enables people to match $ \forall a.a \equiv a $ with $ refl $"? In https://agda.readthedocs.io/en/v2.5.4.1/language/without-k.html#without-k, K-rule is introduced ...