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  2. If and only if - Wikipedia

    en.wikipedia.org/wiki/If_and_only_if

    The corresponding logical symbols are "", "", [6] and , [10] and sometimes "iff".These are usually treated as equivalent. However, some texts of mathematical logic (particularly those on first-order logic, rather than propositional logic) make a distinction between these, in which the first, ↔, is used as a symbol in logic formulas, while ⇔ is used in reasoning about those logic formulas ...

  3. Independence-friendly logic - Wikipedia

    en.wikipedia.org/wiki/Independence-friendly_logic

    Independence-friendly logic (IF logic; proposed by Jaakko Hintikka and Gabriel Sandu [] in 1989) [1] is an extension of classical first-order logic (FOL) by means of slashed quantifiers of the form (/) and (/), where is a finite set of variables.

  4. Syntax (logic) - Wikipedia

    en.wikipedia.org/wiki/Syntax_(logic)

    In logic, syntax is anything having to do with formal languages or formal systems without regard to any interpretation or meaning given to them. Syntax is concerned with the rules used for constructing, or transforming the symbols and words of a language, as contrasted with the semantics of a language which is concerned with its meaning.

  5. Well-formed formula - Wikipedia

    en.wikipedia.org/wiki/Well-formed_formula

    The formulas will be certain expressions (that is, strings of symbols) over this alphabet. The formulas are inductively defined as follows: Each propositional variable is, on its own, a formula. If φ is a formula, then ¬φ is a formula. If φ and ψ are formulas, and • is any binary connective, then ( φ • ψ) is a formula.

  6. First-order logic - Wikipedia

    en.wikipedia.org/wiki/First-order_logic

    There are two key types of well-formed expressions: terms, which intuitively represent objects, and formulas, which intuitively express statements that can be true or false. The terms and formulas of first-order logic are strings of symbols, where all the symbols together form the alphabet of the language.

  7. List of set identities and relations - Wikipedia

    en.wikipedia.org/wiki/List_of_set_identities_and...

    Formulas for binary set operations ⋂, ⋃, \, and ∆ [ edit ] In the left hand sides of the following identities, L {\displaystyle L} is the L eft most set and R {\displaystyle R} is the R ight most set.

  8. Today’s NYT ‘Strands’ Hints, Spangram and Answers ... - AOL

    www.aol.com/today-nyt-strands-hints-spangram...

    Move over, Wordle and Connections—there's a new NYT word game in town! The New York Times' recent game, "Strands," is becoming more and more popular as another daily activity fans can find on ...

  9. Löb's theorem - Wikipedia

    en.wikipedia.org/wiki/Löb's_theorem

    If and are formulas, then so are , , , , and A modal sentence is a formula in this syntax that contains no propositional variables. The notation ⊢ A {\displaystyle \vdash A} is used to mean that A {\displaystyle A} is a theorem.