Questions tagged [formal-systems]

A formal system is broadly defined as any well-defined system of abstract thought based on the model of mathematics. (Def: http://en.m.wikipedia.org/wiki/Formal_system)

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Is 'ismorphism/meaning in formal systems' related to 'domain vs. implementation' in software? [closed]

Is there any relation between these things and, if so, what could I read to learn more? (What I think is) the sometimes-accepted notion of truth in a formal system, e.g. proven statements are true if ...
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Why does natural deduction get its name?

For example, I want to prove $\psi$ from the assumption $\{\varphi,\varphi\to\psi\}$ , the "most natural" proof would be: $\varphi$ $\varphi\to\psi$ $\psi$(MP) But using natural deduction, I ...
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Are ZFC and Formal Number theory already built upon the intuitive notion of set and natural number?

These two theories are known to be first-order theories. And the definition of the first-order logic typically involves something like "set of symbols $a_1, a_2, a_3...$", which already ...
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Reference for basic metatheory of Martin-Löf type theory

Section A.4 of the HoTT book states that the metatheoretic properties of Martin-Löf type theory (such as normalization and canonicity properties) can be proved using “standard techniques from type ...
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What makes a set theory?

So many things get called "set theory" that I'm no longer sure the term is meaningful. This isn't helped by the rather vague notion of "formalizable in ZFC" used to avoid detailed ...
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What does it really mean for a formal system to be consistent?

As far as I understand, asserting that a formal system $T$ is consistent means that there does not exist a sentence $\varphi$, expressed in the language of $T$, such that $T$ proves $\varphi$ and $T$ ...
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Is there a Turing degree/number of unknowns combination beyond which Diophantine equations are independent of PA?

Is there a certain limit in terms of Turing degree and # of unknowns beyond which Diophantine equations (for positive integer solutions) are independent of PA? Specifically, is it meaningful to talk ...
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Is Kleene's realizability recursive?

Kleene introduced realizability as a practical semantical interpretation of Heyting Arithmetic (see link for definition). The key result he proved is that provability of $\varphi$ in HA implies the ...
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Why can't we add a self-consistency axiom to an already consistent system?

Gödel's incompleteness tells us no consistent formal system can prove its own consistency. I understand that we can add an axiom to formal system $A$ stating "$A$ is consistent" and get a ...
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Is it coherent to treat the C programming language as a formal system?

In mathematical logic, a formal system is a structure which includes, amongst other things, a set of axioms, and which is able to determine the truth or falsehood of statements with respect to those ...
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Definition of Locus in Synthetic Geometry?

How is "locus" defined in Euclidean geometry? I know that locus is defined as a set of all points satisfying a certain condition. But how do we define "locus" within an axiomatic ...
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How does the finitely axiomatized formalization of predicate logic correspond to natural deduction for predicate logic?

I'm really interested in using Metamath, but Metamath comes with a funky version of predicate logic. Substitution is not allowed in Metamath, so Metamath employs Tarski's system S2 which is "...
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Given a formal system, determines if 4+3 = 7 is consistent

Given the formal system below: Language:$$\left\{ *,\blacksquare ,\blacklozenge \right\}$$ Syntax: $$ <s>::=<star>,"\blacksquare ",<star>,"\blacklozenge ",\ <star> $$ $$ <...
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Representing first order sentences as conceptual graphs

Here are three first order axioms that represents a part of a mereology theory. Reflexivity $\forall x : part(x,x)$ Antisymmetry $\forall x \forall y : ((part(x,y) \land part(y,x)) \implies (x = y))$ ...
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Is the decidability of all possible axiomatizations equivalent to decidability?

Introduction This is a weird take on a few different topics in logic, so bear with me. To frame this question, consider that "axiomatization" is to "theory" as "...
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How do we classify the obvious fact that $A \xrightarrow{gf} C$ can be decomposed into two arrows? Is it just notational?

The following image is of an app I'm working on called "Abstract Spacecraft". It will allow you to make logical rules and also apply them to diagrams at the click of a button, should the ...
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Generalization of nonexpressibility of solutions

Are there any ideas/areas of math that generalize the idea of when a solution to a question can be expressed in some given formal system? Something that (at least in spirit) covers results like No ...
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Help with metalogic induction proof involving string parsing

I have a formal language (basically language of first order logic) in which Wffs are defined by following. String $A$ is a Wff if it satisfies one of: $A$ is atomic $A \equiv (\lnot B)$ and $B$ is a ...
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Do we have to resort to intuition at the very root of our thinking?

Formal first order logic is the foundation of ZFC set theory. This gives me the impression that a theoretical system has to be based on a formal logical system, with its own axioms and deduction rules....
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Why isn't there an app that allows you to enter in all the rules of a given formal system so that the app supports all formal systems of math?

I'm jumping around between articles about ETCS to Simple TT to Calculus of Constructions wondering what my app should focus on. I'm wondering, why there isn't yet a software app in which you can ...
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Can you give an example of a non-formal system?

A formal system is defined as an abstract structure used for inferring theorems from axioms according to a set of rules (from Wikipedia). Language, logic and mathematics are considered as formal ...
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Essential undecidability of binary string arithmetic

The weak theory of concatenation of binary strings is essentially undecidable.1 Is Presburger arithmetic with two successors (one for each letter) essentially undecidable? Formally, consider the ...
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Precise statement of the syntactic category of a logic/type theory, in maximum generality?

I've been trying to understand the notion of syntactic category for a type theory/logic. This entry in the ncatlab is the closest I've found to a clear explanation. It seems like a fairly good article,...
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Simplest set of axioms and inference rules for first-order logic?

I'm interested in finding the "simplest" formulation of first-order logic. To be precise, what formulation of first-order logic has the fewest total axioms (or axiom schemas, henceforth just ...
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How to write "the set of all walks of a graph" in formal logic notation?

I have this question on the CS stackexchange to figure out how to model "a walk of a graph" in a custom formal language. I think the problem is that there is not just one walk of a graph but ...
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How do you formalize this reasoning?

There is this simple number theory problem which says "how many 4 digit numbers that are divisible by 3 and whose digits exclude 2, 4, 6 and 9 exist?" the solution is quite intuitive: each ...
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Axiom scheme for mathematical induction in formal axiom system for Peano Arithmetic

I'm reading the book "Gödel's incompleteness theorems" by Smullyan. (I found it online here: https://isidore.co/calibre/get/pdf/5823). In Chapter III he explains the Axiom System for Peano ...
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What is a precise definition of soundness?

I'm trying to better understand soundness, especially in contrast to semantic consistency. Here is what I've put together so far: Soundness: A theory is sound if all theorems are true under all ...
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Is it possible to create a "hack-proof" system?

Various organizations, such as DARPA, have purported to create virtually "hack-proof" software systems using mathematical techniques such as formal verification. In short, the idea is ...
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Is there any technical, mathematical or logical, terminology for a set of propositions, all of which cannot be True at the same time.

As the question states, what is the technical term (if any) for a set of propositions which cannot all be true at the same time. That is to say, If there is a set, $A${x1, x2, x3, ... , xn} for which ...
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Is it possible to list all hidden lemmas of a proof?

I'm studying Imre Lakatos' Proofs and Refutations for my master's thesis. Currently I address the concept of hidden lemmas, which I understand to mean unstated assumptions of a mathematical proof, ...
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Beta Reduction Constraints

The definition of $β$ reduction is the following : $$(λx.M)N \rightarrow_{β} Μ[x∶=N] $$ So basically we stop treating $x$ as a bound variable and we perform substitution of the now free variable $x$ ...
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Beta Reduction in Lambda Calculus

I came across the definition of beta reduction in Lambda Calculus which is : $$(λx.M)N \rightarrow_β Μ[\space x:= N \space]$$ under the constraint that the $FV(N)$ are still free after the ...
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Godel Escher Bach: Why is a Godel proof-pair representable in TNT?

On page 441, fundamental fact 2 asserts that: The property of forming a proof-pair is testable in BlooP, and consequently, it is represented in TNT by some formula having two free variables. Why is ...
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Formal relationship between rules of inference and the material conditional

I am not $100\%$ clear as to what constitutes the difference between a rule of inference and the material conditional, at least in classical logic. I am using the truth-functional definition of the ...
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Is there a way to study formal systems in general?

I was reading Gödel Escher Bach, and the author explains that mathematics is just an example of something broader: formal systems. So I wonder wether there exists a theory to study formal systems in ...
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Reading Principles of Mathematical Logic by Hilbert

I want to read Principles of Mathematical Logic by Hilbert and Ackermann. However, I don't know if this is an introductory level text. So I was wondering, is there some background one should have ...
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Describing all formal theory theorems problem

I'm having problems understanding how this works so I'll provide detally explained problem but I'd like if someone could explain it somehow simpler or write it out more step by step than what I'll ...
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Is it possible to add computational facilities to otherwise "mathematical" formal systems by adjoining identities to types?

The following thought has been on my mind for years. Think of $\mathbb{N}$ as the type of all well-formed expressions representing natural numbers. And think of $$\tilde{\mathbb{N}} := \frac{\mathbb{N}...
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What differences and relation are between proof systems and deductive systems? [duplicate]

https://en.wikipedia.org/wiki/Proof_calculus says A proof system includes the components: Language: The set of formulas admitted by the system, for example, propositional logic or first-order logic. ...
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What's up with the Sheffer stroke axiom?

While reading some old paper on the foundations of set theory, I came across a symbol $\mid$ that I eventually determined was the Sheffer stroke, which is a fancy word for NAND. Wikipedia, and also ...
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Implementing sets in $\lambda$-calculus

Both Set theory and $\lambda$-calculus are considered to be valid foundations for mathematics. Since these are both equivalent (in the sense that any structure that can be implemented in set theory ...
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Why doesn't this show that first-order Peano arithmetic is consistent?

SOME PRELIMINARIES: Predicate logic is consistent and complete. In other words, (i) for a closed formula $F$ in predicate calculus with equality and functions, $\vdash F$ if and only if $\,\vDash F$ (...
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What is the definition of a definition?

In mathematical logic or other formal systems, what is the definition of a definition, formally? If "A" is defined as "B", what is the definition of "A" like? Does it ...
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Can inconsistent systems be mathematically interesting/useful?

According to the top answer to this question: Doing mathematics we often have an idea of an object that we wish to represent formally, this is a notion. We then write axioms to describe this notion ...
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What are the relations and differences between formal systems, rewriting systems, formal grammars and automata?

I learned from Herre & Schroeder-Heister's "Formal Languages and Systems" that A formal system is based on a formal language $L$, endowing it with a consequence operation $C: 2^L\to 2^...
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Is this property of derivation relation equivalent to idempotence?

In Herre & Schroeder-Heister's "Formal Languages and Systems", on p6, A formal system is based on a formal language L, endowing it with a consequence operation C. This operation C can ...
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What is compactness for a deductive system?

In Herre & Schroeder-Heister's "Formal Languages and Systems", on p6, It (i.e. a consequential operation) is called a deductive system, if the consequences of a set X can be obtained ...
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Is the semantics of a first order logic system defined as part of the first order logic system?

Does a first order logic system consist only of a first order language a first order deductive system? Is a first order logic system nothing more than a formal system? Is the semantics of a first ...
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Is linear algebra a formal system?

By a formal system I mean a system for inferring theorems from axioms according to a set of rules. Essentially I wonder, whether a linear algebra could be viewed as some particular set of axioms from ...
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