1.NounA function between two sets
A
{\displaystyle A}
and
B
{\displaystyle B}
, with the former being a subset of the latter, that maps elements from
A
{\displaystyle A}
to the corresponding elements of
B
{\displaystyle B}
(
ι
:
A
→
B
,
ι
(
x
)
=
x
{\displaystyle \iota :A\to B,\iota (x)=x}
).