Formal languages | Formal systems | Proof theory

Formal proof

In logic and mathematics, a formal proof or derivation is a finite sequence of sentences (called well-formed formulas in the case of a formal language), each of which is an axiom, an assumption, or follows from the preceding sentences in the sequence by a rule of inference. It differs from a natural language argument in that it is rigorous, unambiguous and mechanically verifiable. If the set of assumptions is empty, then the last sentence in a formal proof is called a theorem of the formal system. The notion of theorem is not in general effective, therefore there may be no method by which we can always find a proof of a given sentence or determine that none exists. The concepts of Fitch-style proof, sequent calculus and natural deduction are generalizations of the concept of proof. The theorem is a syntactic consequence of all the well-formed formulas preceding it in the proof. For a well-formed formula to qualify as part of a proof, it must be the result of applying a rule of the deductive apparatus (of some formal system) to the previous well-formed formulas in the proof sequence. Formal proofs often are constructed with the help of computers in interactive theorem proving (e.g., through the use of proof checker and automated theorem prover). Significantly, these proofs can be checked automatically, also by computer. Checking formal proofs is usually simple, while the problem of finding proofs (automated theorem proving) is usually computationally intractable and/or only semi-decidable, depending upon the formal system in use. (Wikipedia).

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This video introduces the mathematical proof method of direct proof provides an example of a direct proof. mathispower4u.com

From playlist Symbolic Logic and Proofs (Discrete Math)

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This video introduces the common methods of mathematical proofs and provides a basic example of a direct proof. mathispower4u.com

From playlist Symbolic Logic and Proofs (Discrete Math)

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From playlist Math Major Basics

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From playlist Proofs

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From playlist Parallel Lines and a Transversal

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From playlist Parallel Lines and a Transversal

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From playlist Parallel Lines and a Transversal

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From playlist Math Major Basics

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From playlist Bourbaki - 21 juin 2014

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From playlist 2023 Machine Assisted Proofs Workshop

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3 - Kick-off afternoon : Thomas Hales, Formalizing the proof of the Kepler Conjecture

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Micaela Mayero - Overview of real numbers in theorem provers: application with real analysis in Coq

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Related pages

Natural deduction | Interpretation (logic) | Proof (truth) | Proof assistant | De Bruijn Factor | Theorem | Formal verification | Mathematical proof | Well-formed formula | Formal language | Sequence | Sequent calculus | Proof theory | Mathematics | Set (mathematics) | Axiomatic system | Fitch notation | Proof calculus | Axiom | Effective method | Structure (mathematical logic) | Rule of inference | Formal system | Follows from | String (computer science)