1 The logical connective combining two statements or formulas P and Q in such a way that the outcome is true if both P and Q are true or if both are false, as shown in the table. P and Q are said to be equivalent. The connective can be read as “if and only if” or “iff”, and is usually denoted by one of the following symbols:
≡ ↔ <—> ⇔
See also exclusive-NOR gate, propositional calculus.
2 A relationship between objects that are operationally or structurally indistinguishable, e.g. in combinational circuits, graphs, or grammars. Equivalence is less strong than identity or equality but much more useful in practice. See also machine equivalence.