Félix Cabello Sánchez is Professor of Mathematics at the Universidad de Extremadura. He is co-author of the monograph Separably Injective Banach Spaces (2016).

Preliminaries; 1. Complemented subspaces of Banach spaces; 2. The language of homology; 3. Quasilinear maps; 4. The functor Ext and the homology sequences; 5. Local methods in the theory of twisted sums; 6. Fraissé limits by the pound; 7. Extensions of operators, isomorphisms and isometries; 8. Extension of C(K)-valued operators; 9. Singular exact sequences; 10. Back to Banach space theory; Bibliography; Index.