CentralNotice From Wikipedia, the free encyclopedia Jump to: navigation , search "Iff" redirects here. For other uses, see IFF (disambiguation) . "↔" redirects here. It is not to be confused with Bidirectional traffic . This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. (July 2013) ↔⇔≡ Logical symbols representing iff Transformation rules Propositional calculus Rules of inference Modus ponens / Modus tollens Biconditional introduction / elimination Conjunction introduction / elimination Disjunction introduction / elimination Disjunctive / Hypothetical syllogism Constructive / Destructive dilemma Absorption Modus ponendo tollens Rules of replacement Associativity Commutativity Distributivity Double ne...