In
mathematics, an
index set is a set whose members label (or index) members of another set. For instance, if the elements of a
set A may be
indexed or
labeled by means of a set
J, then
J is an index set. The indexing consists of a
surjective function from
J onto
A and the indexed collection is typically called an
(indexed) family, often written as (
Aj)
j∈J.