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 symbols
≡ ↔ < - > < = >
See also prepositional 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.