Example image of eyePlorer eyePlorer map for 'If and only if': Logic Logical biconditional Logical connective Mathematics Philosophy Material conditional Necessary and sufficient condition Well-formed formula Truth table XNOR gate First-order logic Mathematical logic Metalogic Propositional calculus Logical equality Contraposition Formal system Proof theory Logical disjunction Truth function John L. Kelley Mathematician Paul Halmos Logical equivalence Use–mention distinction Willard Van Orman Quine Definition Universal quantification Group (mathematics) Logical conjunction Exclusive or Mathematical jargon Domain of discourse Agoh–Giuga conjecture Almost prime Biconditional introduction Chinese hypothesis Commensurability (mathematics) Compact complement topology Complement graph Crossing number (graph theory) De Morgan's laws Desargues' theorem Either–or topology Fermat's theorem on sums of two squares Forbidden graph characterization Huge cardinal Inequality of arithmetic and geometric means Kuroda normal form Locally constant function