Also known as categorical sum
In category theory, the coproduct, or categorical sum, is a construction which includes as examples the disjoint union of sets and of topological spaces, the free product of groups, and the direct sum of modules and vector spaces. The coproduct of a family of objects is essentially the "least specific" object to which each object in the family admits a morphism. It is the category-theoretic dual notion to the categorical product, which means the definition is the same as the product but with all arrows reversed. Despite this seemingly innocuous change in the name and notation, coproducts can b
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Article · 日本語
圏論において、余積（よせき、双対積、双対直積、英: coproduct）あるいは圏論的和（わ、直和、英: sum, direct sum）は、集合の直和、位相空間の直和、群の自由積、加群やベクトル空間の直和などを例として含む圏論的構成である。対象の族の余積は本質的に、族の各対象がそこへの射をもつような「最も固有的でない (least specific)」対象である。それは圏論的（直）積の圏論的双対概念であり、これは定義がすべての矢印を逆にすることを除けば積と同じであることを意味する。名前と表記の一見無害な変化にもかかわらず、余積は積と劇的に異なり得るし、典型的にはそうなる。
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