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:
“All men, in the abstract, are just and good; what hinders them, in the particular, is, the momentary predominance of the finite and individual over the general truth. The condition of our incarnation in a private self, seems to be, a perpetual tendency to prefer the private law, to obey the private impulse, to the exclusion of the law of the universal being.”
—Ralph Waldo Emerson (1803–1882)
“Man was born rich, or inevitably grows rich by the use of his faculties; by the union of thought with nature. Property is an intellectual proposition.”
—Ralph Waldo Emerson (1803–1882)