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  2. Proof by contradiction - Wikipedia

    en.wikipedia.org/wiki/Proof_by_contradiction

    Formally the law of non-contradiction is written as ¬(P ∧ ¬P) and read as "it is not the case that a proposition is both true and false". The law of non-contradiction neither follows nor is implied by the principle of Proof by contradiction. The laws of excluded middle and non-contradiction together mean that exactly one of P and ¬P is true.

  3. Contradiction - Wikipedia

    en.wikipedia.org/wiki/Contradiction

    From this, Post was able to derive the following definition of inconsistency—without the use of the notion of contradiction: Definition. A system will be said to be inconsistent if it yields the assertion of the unmodified variable p [S in the Newman and Nagel examples].

  4. List of logic symbols - Wikipedia

    en.wikipedia.org/wiki/List_of_logic_symbols

    The following table lists many common symbols, together with their name, how they should be read out loud, and the related field of mathematics. Additionally, the subsequent columns contains an informal explanation, a short example, the Unicode location, the name for use in HTML documents, [ 1 ] and the LaTeX symbol.

  5. Contraposition - Wikipedia

    en.wikipedia.org/wiki/Contraposition

    Since nothing is said in the definition of contraposition with regard to the predicate of the inferred proposition, it is permissible that it could be the original subject or its contradictory. This is in contradistinction to the form of the propositions of transposition, which may be material implication, or a hypothetical statement.

  6. Law of noncontradiction - Wikipedia

    en.wikipedia.org/wiki/Law_of_noncontradiction

    In logic, the law of non-contradiction (LNC) (also known as the law of contradiction, principle of non-contradiction (PNC), or the principle of contradiction) states that contradictory propositions cannot both be true in the same sense at the same time, e. g. the two propositions "the house is white" and "the house is not white" are mutually exclusive.

  7. Proof of impossibility - Wikipedia

    en.wikipedia.org/wiki/Proof_of_impossibility

    One of the widely used types of impossibility proof is proof by contradiction.In this type of proof, it is shown that if a proposition, such as a solution to a particular class of equations, is assumed to hold, then via deduction two mutually contradictory things can be shown to hold, such as a number being both even and odd or both negative and positive.

  8. Semiotic square - Wikipedia

    en.wikipedia.org/wiki/Semiotic_square

    This is where the principle of difference is brought into play: every element in a system is defined by its differences from the other elements. In most modes of interpretation, the S-axis is a hyponym of the ~S-axis. The ~S 1 element combines aspects of S 1 and S 2 and is also contradictory to S 1. The ~S 2 element contains aspects of neither ...

  9. Square of opposition - Wikipedia

    en.wikipedia.org/wiki/Square_of_opposition

    In these relations, the particular is the subaltern of the universal, which is the particular's superaltern. For example, if 'every man is white' is true, its contrary 'no man is white' is false. Therefore, the contradictory 'some man is white' is true. Similarly the universal 'no man is white' implies the particular 'not every man is white ...