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  2. If and only if - Wikipedia

    en.wikipedia.org/wiki/If_and_only_if

    The biconditional is true in two cases, where either both statements are true or both are false. The connective is biconditional (a statement of material equivalence), [2] and can be likened to the standard material conditional ("only if", equal to "if ... then") combined with its reverse ("if"); hence the name. The result is that the truth of ...

  3. 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.

  4. List of rules of inference - Wikipedia

    en.wikipedia.org/wiki/List_of_rules_of_inference

    Biconditional introduction All rules use the basic logic operators. A complete table of "logic operators" is shown by a truth table , giving definitions of all the possible (16) truth functions of 2 boolean variables ( p , q ):

  5. Contraposition - Wikipedia

    en.wikipedia.org/wiki/Contraposition

    The symbol for material implication signifies the proposition as a hypothetical, or the "if–then" form, e.g. "if P, then Q". The biconditional statement of the rule of transposition (↔) refers to the relation between hypothetical (→) propositions , with each proposition including an antecedent and consequential term.

  6. Hypothetical syllogism - Wikipedia

    en.wikipedia.org/wiki/Hypothetical_syllogism

    An invalid hypothetical syllogism either affirms the consequent (fallacy of the converse) or denies the antecedent (fallacy of the inverse). A pure hypothetical syllogism is a syllogism in which both premises and the conclusion are all conditional statements. The antecedent of one premise must match the consequent of the other for the ...

  7. Rule of inference - Wikipedia

    en.wikipedia.org/wiki/Rule_of_inference

    Biconditional introduction / elimination; ... If premises are left unsatisfied in the derivation, then the derivation is a proof of a hypothetical statement: ...

  8. Glossary of logic - Wikipedia

    en.wikipedia.org/wiki/Glossary_of_logic

    A hypothetical construct in modal logic representing a way things could not possibly be, used to explore concepts of necessity and possibility. impredicative definition A definition that refers to a set that includes the entity being defined, often leading to paradoxes in naive set theories. inclusive disjunction

  9. Biconditional introduction - Wikipedia

    en.wikipedia.org/wiki/Biconditional_introduction

    In propositional logic, biconditional introduction [1] [2] [3] is a valid rule of inference. It allows for one to infer a biconditional from two conditional statements . The rule makes it possible to introduce a biconditional statement into a logical proof .