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Sentences are then built up out of atomic sentences by applying connectives and quantifiers. A set of sentences is called a theory; thus, individual sentences may be called theorems. To properly evaluate the truth (or falsehood) of a sentence, one must make reference to an interpretation of the theory.
A proof is sufficient evidence or a sufficient argument for the truth of a proposition. [1] [2] [3] [4]The concept applies in a variety of disciplines, [5] with both the nature of the evidence or justification and the criteria for sufficiency being area-dependent.
The corresponding conditional of a valid argument is a logical truth and the negation of its corresponding conditional is a contradiction. The conclusion is a necessary consequence of its premises. An argument that is not valid is said to be "invalid". An example of a valid (and sound) argument is given by the following well-known syllogism:
The definition of a formal proof is intended to capture the concept of proofs as written in the practice of mathematics. The soundness of this definition amounts to the belief that a published proof can, in principle, be converted into a formal proof. However, outside the field of automated proof assistants, this is rarely done in practice.
A sentence is said to be a logical consequence of a set of sentences, for a given language, if and only if, using only logic (i.e., without regard to any personal interpretations of the sentences) the sentence must be true if every sentence in the set is true.
Given any number , we seek to prove that there is a prime larger than . Suppose to the contrary that no such p exists (an application of proof by contradiction). Then all primes are smaller than or equal to n {\displaystyle n} , and we may form the list p 1 , … , p k {\displaystyle p_{1},\ldots ,p_{k}} of them all.
It is based on the idea that the sentences constituting the premises and conclusions have to be interpreted in order to determine whether the argument is valid. [13] [6] [5] This means that one ascribes semantic values to the expressions used in the sentences, such as the reference to an object for singular terms or to a truth-value for atomic ...
The word ‘proof’ comes from the Latin word probare, [3] which means “to test”. The earliest use of proofs was prominent in legal proceedings. A person with authority, such as a nobleman, was said to have probity, which means that the evidence was by his relative authority, which outweighed empirical testimony.