Derived Functors
Handbook guide to Derived Functors, covering core definitions, key results, formulas, reasoning methods and worked examples in graduate abstract algebra.
Every page in the KEVOS library tagged derived functors. 8 pages.
Handbook guide to Derived Functors, covering core definitions, key results, formulas, reasoning methods and worked examples in graduate abstract algebra.
Chain and cochain complexes, cycles and boundaries, homology as a functor, and the abelian category of complexes.
Chain homotopy between chain maps, homotopy equivalence, the comparison theorem for projective resolutions, and independence of derived functors from the chosen resolution.
Restriction and extension of scalars, induced and coinduced modules, the change-of-rings theorems, and the associated spectral sequences.
Computing Ext by resolving either variable, the double complex proof that the two agree, and the practical consequences for choosing a computation.
The long exact sequence associated to a short exact sequence of complexes, construction of the connecting homomorphism, naturality, and the standard applications.
Derivation of the long exact sequences of derived functors via the horseshoe lemma, their naturality, dimension shifting and the standard computational patterns.
The Yoneda description of Ext^n by n-fold extensions, the equivalence relation, splicing as composition, and the Yoneda product.