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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. Truth table - Wikipedia

    en.wikipedia.org/wiki/Truth_table

    p iff q: Epq: Logical biconditional: if p then q; and if q then p: 10 ... The truth table for p XNOR q (also written as pq, Epq, p = q, or pq) is as follows ...

  4. Logical equivalence - Wikipedia

    en.wikipedia.org/wiki/Logical_equivalence

    In logic and mathematics, statements and are said to be logically equivalent if they have the same truth value in every model. [1] The logical equivalence of p {\displaystyle p} and q {\displaystyle q} is sometimes expressed as pq {\displaystyle p\equiv q} , p :: q {\displaystyle p::q} , E p q {\displaystyle {\textsf {E}}pq} , or p q ...

  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. List of rules of inference - Wikipedia

    en.wikipedia.org/wiki/List_of_rules_of_inference

    With this premise, we also conclude that q=T, pq=T, etc. as shown by columns 9–15. The column-11 operator (IF/THEN), shows Modus ponens rule: when pq=T and p=T only one line of the truth table (the first) satisfies these two conditions. On this line, q is also true. Therefore, whenever pq is true and p is true, q must also be true.

  7. Necessity and sufficiency - Wikipedia

    en.wikipedia.org/wiki/Necessity_and_sufficiency

    The assertion that Q is necessary for P is colloquially equivalent to "P cannot be true unless Q is true" or "if Q is false, then P is false". [9] [1] By contraposition, this is the same thing as "whenever P is true, so is Q". The logical relation between P and Q is expressed as "if P, then Q" and denoted "PQ" (P implies Q).

  8. Propositional calculus - Wikipedia

    en.wikipedia.org/wiki/Propositional_calculus

    Since truth tables have 2 n lines for n variables, they can be tiresomely long for large values of n. [39] ... (p iff q) is equiv. to either (p and q are true) or ...

  9. Logical equality - Wikipedia

    en.wikipedia.org/wiki/Logical_equality

    The truth table of p EQ q (also written as p = q, pq, Epq, pq, or p == q) is as follows: The Venn diagram of A EQ B (red part is true) Logical equality p q