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  2. If and only if - Wikipedia

    en.wikipedia.org/wiki/Iff

    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. List of logic symbols - Wikipedia

    en.wikipedia.org/wiki/List_of_logic_symbols

    if and only if, iff, xnor propositional logic, Boolean algebra: is true only if both A and B are false, or both A and B are true. Whether a symbol means a material biconditional or a logical equivalence, depends on the author’s style.

  4. Contraposition - Wikipedia

    en.wikipedia.org/wiki/Contraposition

    Since the statement and the converse are both true, it is called a biconditional, and can be expressed as "A polygon is a quadrilateral if, and only if, it has four sides." (The phrase if and only if is sometimes abbreviated as iff.) That is, having four sides is both necessary to be a quadrilateral, and alone sufficient to deem it a quadrilateral.

  5. Logical biconditional - Wikipedia

    en.wikipedia.org/wiki/Logical_biconditional

    Venn diagram of (true part in red) In logic and mathematics, the logical biconditional, also known as material biconditional or equivalence or biimplication or bientailment, is the logical connective used to conjoin two statements and to form the statement "if and only if" (often abbreviated as "iff " [1]), where is known as the antecedent, and the consequent.

  6. Logical equivalence - Wikipedia

    en.wikipedia.org/wiki/Logical_equivalence

    This statement expresses the idea "' if and only if '". In particular, the truth value of p ↔ q {\displaystyle p\leftrightarrow q} can change from one model to another. On the other hand, the claim that two formulas are logically equivalent is a statement in metalanguage , which expresses a relationship between two statements p {\displaystyle ...

  7. Identification friend or foe - Wikipedia

    en.wikipedia.org/wiki/Identification_friend_or_foe

    An IFF test set used by a United States Air Force avionics technician technical sergeant for testing transponders on aircraft in 2001. Model XAE IFF kit, the first radio recognition IFF system in the U.S. Identification, friend or foe (IFF) is a combat identification system designed for command and control.

  8. Woman Missing After Not Getting on Connecting Flight Sent ...

    www.aol.com/lifestyle/woman-missing-not-getting...

    Hannah Kobayashi, from Hawaii, has been missing since she landed in Los Angeles on Friday, Nov. 8. A Hawaii woman who has been missing since she failed to board a connecting flight in Los Angeles ...

  9. Talk:If and only if/Archive 1 - Wikipedia

    en.wikipedia.org/wiki/Talk:If_and_only_if/Archive_1

    There is a difference between iff and a logical biconditional-- iff ought to imply only a "necessary condition", but not a "sufficient condition". It is amusing how this subject, in contrast to other subjects in the field, is such a visible motive for controversy.