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 or follows from the preceding sentences in the sequence by a rule of inference. The last sentence in the sequence is a theorem of a 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 concept of natural deduction is a generalization 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 formulae in the proof sequence.

Formal proofs often are constructed with the help of computers in interactive theorem proving. 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.

### Other articles related to "formal proof, formal, proof":

**Formal Proof**

... But this manoeuvre of itself cannot contain any

**formal proof**of a necessary quantitative relationship between values and prices, nor a

**formal proof**that capitals ... In that case, there is again no

**formal proof**of any necessary relationship between values and prices, and Marx's manuscript really seems an endless, pointless theoretical detour leading nowhere ...

**Formal Proof**

... First we prove ¬(p ∨ q) ⇔ (¬p) ∧ (¬q) ... p q p ∨ q ¬(p ∨ q) ¬p ¬q (¬p) ∧ (¬q) 0 ... Since the values in the 4th and last columns are the same for all rows (which cover all possible truth value assignments to the variables), we can conclude that the two expressions are logically equivalent ...

**Formal Proof**- Background - Interpretations

... An interpretation of a

**formal**system is the assignment of meanings to the symbols, and truth-values to the sentences of a

**formal**system ... The study of interpretations is called

**formal**semantics ...

... Because statements of a

**formal**theory are written in symbolic form, it is possible to mechanically verify that a

**formal proof**from a finite set of axioms is valid ... This task, known as automatic

**proof**verification, is closely related to automated theorem proving ... is that instead of constructing a new

**proof**, the

**proof**verifier simply checks that a provided

**formal proof**(or, in instructions that can be followed ...

### Famous quotes containing the words proof and/or formal:

“If any doubt has arisen as to me, my country [Virginia] will have my political creed in the form of a “Declaration &c.” which I was lately directed to draw. This will give decisive *proof* that my own sentiment concurred with the vote they instructed us to give.”

—Thomas Jefferson (1743–1826)

“Two clergymen disputing whether ordination would be valid without the imposition of both hands, the more *formal* one said, “Do you think the Holy Dove could fly down with only one wing?””

—Horace Walpole (1717–1797)