\frownThe \frown symbol is used to denote a concave arc or a frown shape in mathematical expressions. It is often used in geometry to represent angles or arcs that are concave in nature.
Denotes a concave angle at point B between lines AB and BC.
\angle ABC \frownRepresents a concave arc over points A and B.
\overarc{AB} \frownIndicates a relation or operation between x and y that is concave in nature.
x \frown y