 Also in mathematical expressions in general, parentheses are used to indicate grouping (that is, which parts belong together) when necessary to avoid ambiguities, or for the sake of clarity.For example, in the formula (εη)"X" = ε"Cod ηX"η"X", used in the definition of composition of two natural transformations, the parentheses around εη serve to indicate that the indexing by "X" is applied to the composition εη, and not just its last component η.The arguments to a function are frequently surrounded by brackets