A bidirectional arrow accent placed beneath text to indicate equivalence or reversible relationships in algebra and category theory.
Examples
Reversible transformation between states
A \underleftrightarrow{\text{transform}} B
Bidirectional vector between points
\underleftrightarrow{AB} = \underleftrightarrow{BA}
Equilibrium reaction in chemistry
N_2 + 3H_2 \underleftrightarrow{\text{heat}} 2NH_3