18C10 Theories (e.g. algebraic theories), structure, and semantics [See also <a href="#code:03G30">03G30</a>]

18C15 Triples (= standard construction, monad or triad), algebras for a triple, homology and derived functors for triples [See also <a href="#code:18Gxx">18Gxx</a>]

18C20 Algebras and Kleisli categories associated with monads

18C35 Accessible and locally presentable categories

18C50 Categorical semantics of formal languages [See also <a href="#code:68Q55">68Q55</a>, <a href="#code:68Q65">68Q65</a>]

18C99 None of the above, but in this section

18D05 Double categories, $2$-categories, bicategories and generalizations

18D10 Monoidal categories (= multiplicative categories), symmetric monoidal categories, braided categories [See also <a href="#code:19D23">19D23</a>]

18D15 Closed categories (closed monoidal and Cartesian closed categories, etc.)

18D20 Enriched categories (over closed or monoidal categories)

18D25 Strong functors, strong adjunctions

18D35 Structured objects in a category (group objects, etc.)

18D50 Operads [See also <a href="#code:55P48">55P48</a>]

18D99 None of the above, but in this section

18E10 Exact categories, abelian categories

18E20 Embedding theorems [See also <a href="#code:18B15">18B15</a>]

18E30 Derived categories, triangulated categories

18E40 Torsion theories, radicals [See also <a href="#code:13D30">13D30</a>, <a href="#code:16S90">16S90</a>]

18E99 None of the above, but in this section

18F10 Grothendieck topologies [See also <a href="#code:14F20">14F20</a>]

18F15 Abstract manifolds and fiber bundles [See also <a href="#code:55Rxx">55Rxx</a>, <a href="#code:57Pxx">57Pxx</a>]

18F30 Grothendieck groups [See also <a href="#code:13D15">13D15</a>, <a href="#code:16E20">16E20</a>, <a href="#code:19Axx">19Axx</a>]

18F99 None of the above, but in this section

18Gxx Homological algebra [See also <a href="#code:13Dxx">13Dxx</a>, <a href="#code:16Exx">16Exx</a>, <a href="#code:20Jxx">20Jxx</a>, <a href="#code:55Nxx">55Nxx</a>, <a href="#code:55Uxx">55Uxx</a>, <a href="#code:57Txx">57Txx</a>]