Universal Property
In the language of category theory, the direct sum is a coproduct and hence a colimit in the category of left R-modules, which means that it is characterized by the following universal property. For every i in I, consider the natural embedding
which sends the elements of Mi to those functions which are zero for all arguments but i. If fi : Mi → M are arbitrary R-linear maps for every i, then there exists precisely one R-linear map
such that f o ji = fi for all i.
Dually, the direct product is the product.
Read more about this topic: Direct Sum Of Modules
Famous quotes containing the words universal and/or property:
“It is impossible that anything so natural, so necessary, and so universal as death should ever have been designed by Providence as an evil to mankind.”
—Jonathan Swift (1667–1745)
“Personal rights, universally the same, demand a government framed on the ratio of the census: property demands a government framed on the ratio of owners and of owning.”
—Ralph Waldo Emerson (1803–1882)