\xLeftrightarrow{abc}The command \xLeftrightarrow{abc} is used to create an extensible double-headed arrow with text 'abc' above it. This is typically used in mathematical expressions to denote equivalence or a bidirectional relationship between two expressions, with additional context or conditions specified above the arrow.
Indicates that A is equivalent to B under the condition or context 'abc'.
A \xLeftrightarrow{abc} BDenotes that x is equivalent to y as n approaches infinity.
x \xLeftrightarrow{n \to \infty} yShows that P is equivalent to Q by definition, with 'by def' above the arrow.
P \xLeftrightarrow{\text{by def}} Q