Algebra (structure)
Let be a commutative ring. We say that a set
is an
-algebra
if
is an
-module and we have a
-bilinear mapping of
into
, denoted multiplicatively. That is, we have a multiplication between elements of
,
and between elements of
and elements of
such that for any
,
,
and
We identify elements
of
with the corresponding elements
of
.
Note that multiplication in need not be associative or commutative; however,
the elements of
must commute and associate with all elements of
. We can thus think
of
as an
-module endowed with a certain kind of multiplication.
Equivalently, we can say that
is an
-algebra if it is a not-necessarily-associative ring that contains
as a sub-ring.
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