# Questions tagged [coq]

Coq is an interactive theorem prover based on the Calculus of Inductive Constructions.

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### Why does Coq include let-expressions in its core language

Coq includes let-expressions in its core language. We can translate let-expressions to applications like this: let x : t = v in b ~> (\(x:t). b) v I understand ...
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### formalization of partial function for counting

I need assistance in defining axioms for partial functions in total function theory that is available in Coq. Specifically, I'm looking for a constructive definition of a partial function that ...
55 views

### Defining 2 inductive propositions relying on each other in Coq

I'm pretty beginner in Coq. I want to formalize negative and positive occurrence of an atom in a proposition inside coq the definition is as down below: I want to define this property as an Inductive ...
1k views

### Polymorphism and Inductive datatypes

I'm curious. I've been working on this datatype in OCaml: ...
3k views

### Recursive definitions over an inductive type with nested components

Consider an inductive type which has some recursive occurrences in a nested, but strictly positive location. For example, trees with finite branching with nodes using a generic list data structure to ...
306 views

### Building non-classical logics in Agda & Coq

Is it possible to construct different systems of logic in Coq or Agda? I ask because I'm interested in using a proof assistant to construct (and verify) theorems in things like many-valued logics, ...
406 views

### What is the runtime/time complexity of Coq’s (Dependent) Type Inference?

I remember learning in a class that type inference is decidable but usually takes a long time (e.g. type inference in OCaml is EXPTIME). I was wondering, since Coq allows programs/values themselves to ...
10k views

### Learning Automated Theorem Proving

I am learning Automated Theorem Proving / SMT solvers / Proof Assistants by myself and post a series of questions about the process, starting here. Note that these topics are not easily digested ...
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### Coq stuck on proof for Theorem eqblist_true

I'm stuck on this proof for the theorem eqblist_true. So far what I have is: ...
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### What is different between Set and Type in Coq? [closed]

AFAIU types can be a Set whose elements are programs or a proposition whose elements are Proofs. So based on this understanding: ...
1 vote
197 views

### Is there a tactic to help resolving existential quantifiers in Coq?

I am working on Software Foundations Volume 1 on my own it is its 2019 version by the way, and I have reached to its lesson Inductively Defined Propositions, and there, for almost one month I have ...
1 vote
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### How do program types such as natural numbers figure into the Curry-Howard Isomorphism?

In Coq, the nat, the type of natural numbers, has type Set. By the Curry-Howard Isomorphism, all propositions of type ...
120 views

### What are the differences between LCF's Theorem and Automath's Prop?

How are the fundamental approaches to proving theorems by LCF and Automath different? Considering their modern descendants - Isabelle for LCF and Coq for Automath, both rely on type checking to do ...
1 vote
59 views

### Why discriminate the base case allows me to complete the induction proof?

I have a successful completed proof which used induction. but I essentially proved the goal on the base case by tactic discriminate. Why is this induction proof ...
1 vote
51 views

### why is behaviour of simpl differ so much after a commutative operation and how to inspect simpl?

In Coq, while trying to prove a lemma mult_n_Sm for mult_comm, I have this equation in a proof: ...
52 views

### Why isn't plus_assoc rewriting correctly?

First I have plus_assoc ready. Theorem plus_assoc : forall n m p : nat, n + (m + p) = (n + m) + p. for simplicity we omit the ...
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### Difference between the logic and the type system of a proof assistant?

In Comparing Mathematical Provers (section 4.1), Wiedijk classifies logics and type systems of different proof assistants? I do not see what he means by type system of the assistant. He only says: A ...
162 views

### Understanding the definition of Positivity Constraints in Coq

In Interactive Theorem Proving and Program Development the authors explain constraints on constructors of inductive types in Coq. For inductive type $T$, a constructor must have the form \$t_1 \...
1 vote
59 views

### Instantiating a class with a sig'd type in Coq

I can easily define a class that corresponds to the notion of a "monoidal structure" on a type M via ...
1 vote
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### on coq: Why is the proof complete after proving only for one induction when we have more than one variable?

So I'm learning coq. And I came across the proof for associativity in addition forall (a b c : nat) Appearntly when we do ...
258 views

### How to prove transitivity of < (Software Foundations exercise)?

I'm working through the "Properties of Relations" chapter of Software Foundations, but have got stuck on one of the exercises, lt_trans'': ...
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### What can we have in exchange if we drop subtyping from definition of Calculus of Inductive Constructions?

If we remove subtyping (https://coq.inria.fr/distrib/current/refman/language/cic.html#subtyping-rules) from CIC we will lose some expressive power. But is that power necessary for a programming ...
285 views

### When can the coinduction hypothesis be used?

We can use the induction hypothesis when we are proving a property for a structure that is well-ordered. I am aware that there is a proof for this. When it comes to coinduction, I'm confused. One of ...
197 views

### Stuck on proof in Coq

This is an exercise from Software foundations for my discrete math & functional programming class. I am a little stuck with the end of the code because it works for the first two examples but it ...
282 views

### Is extensionality for coinductive datatypes consistent with Coq's logic?

Given a coinductive datatype, one can usually (always?) define a bisimulation as the largest equivalence relation over it. I would like to add an axiom stating that if two members of the type are ...
266 views

### For proof automation in Coq, when is it appropriate to use canonical structures or Equations instead of Ltac?

There are a few possible approaches to proof automation in modern Coq. Writing proof scripts with Ltac. This is the approach described in http://adam.chlipala.net/cpdt/, which the author uses to ...
195 views

### Proving with co-induction principles

I'm going through Adam Chlipala's "Certified Programming with Dependent Types" (available here for convenience), and I'm a bit stuck at internalizing the introduction of co-induction principle for the ...
329 views

### What types are propositions?

In the propositions-as-types paradigm, we are still faced with the question : what types are propositions ? I currently know 3 different answers : Coq's sort Prop ...
601 views

### How does one know what statements in Coq require Induction?

I was trying to learn Coq using the famous book Software Foundations. In it I found the following: ...
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### How does this use of "apply" in Coq work?

I'm working my way through software foundations. In the Chapter titled "Tactics", I'm able to prove this theorem in Coq: ...
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### An instance when you can eliminate propositional double negation in coq

Suppose st: string -> nat and X stands for the string 'X'. Given the hypothesis ...
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### What are the implications of Lean not having the type Set?

In Coq we have an impredicative base type, called Prop, and a predicative base type, called Set, both of type ...
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### Proving parametricity for Gallina functions

I have the following definitions Definition nat'' {X : Type} := (X -> X) -> X -> X. Definition nat' := forall (X : Type), @nat'' X. And when I wanted to ...
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### What does instantiating existential variables with out of scope variable imply?

I have following unfinished proof of a lemma: ...
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### How CompCert "proves" different things in its codebase

In order to understand examples of formal proofs, I am interested in how CompCert applies "proof" techniques. Specifically, I am wondering what a particular example is of something CompCert "proves" ...
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### Why does substitution terminate?

I'm formalizing some properties of lambda calculus in Coq and I have some problems proving termination of substitution. My terms are defined as: ...
285 views

### Is impredicative Set consistent with the excluded middle?

While studying Coq, I found a few references that impredicative Set might not work well with classical axioms, in particular the axiom of choice. I'm working on a dependent type system based on the ...
566 views

### I don't know how to prove a simple theorem used with fixpoint in Coq

I am a beginner in coq and want to prove the following theorem t1. First I used induction i and destruct j, but it got bogged ...
2k views

### Monadic Second Order Logic for Dummies

I am programmer with a grip on automata, but not on logic. I read in papers that the two are very tightly related. Deterministic Finite Automata (DFA), Tree Automata and Visibly Pushdown Automata are ...
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### positivity condition in Coq/CIC

I am recently learning the theory behind Coq and learnt that positivity condition guarantees termination of the program. But my question is, what would you think of the following definition? ...
301 views

### In Coq, what does it mean to have an inductive type where the right-hand side of ":" is Prop?

I'm new to Coq, and my (rather limited) understanding is that inductive types are like algebraic datatypes in Haskell, so there is a constructor data T = A a with ...
2k views

### Is possible to prove undecidability of the halting problem in Coq?

I was watching the "Five Stages of Accepting Constructive Mathematics" by Andrej Bauer and he says that there is two kinds of proof by contradiction (or two things that mathematicians call proof by ...
1 vote
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### How to prove T Z = Z for binary representation of natural numbers in Coq

I have defined an Inductive in Coq for binary representation of natural numbers as follows: ...
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### Does there exist any work on creating a Real Number/Probability Theory Framework in COQ?

COQ is an interactive theorem prover that uses the calculus of inductive constructions, i.e. it relies heavily on inductive types. Using those, discrete structures like natural numbers, rational ...
431 views

### Type Theory and Principia Mathematica Part IV "Relation Arithmetic"

As type theory is a principle focus of modern computer science, its origins are in Bertrand Russel's theory of types, Principia Mathematica is both the origin of and is expressed in the theory of ...
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### Why are recursive types needed as primitives for proofs in dependent type systems?

I'm relatively new to type theory and dependent programming. I've been studying the calculus of constructions (CoC) and other pure type systems. I'm particularly interested in using it as a proof-...
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### Proving tautology with coq

Currently I have to learn Coq and don't know how to deal with an or : As an example, as simple as it is, I don't see how to prove: ...
578 views

### Proof of equality with destructuring let...in

I have some expression (f n in the example below) returning a tuple. I would like to prove that f n is equal to ...
1 vote