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Adamek and Sousa recently solved the problem of characterizing the subcategories K of a locally $\lambda$-presentable category C which are $\lambda$-orthogonal in C, using their concept of K$\lambda$-pure morphism. We strengthen the latter definition, in order to obtain a characterization of the classes defined by orthogonality with respect to $\lambda$-presentable morphisms (where $f : A \rightarrow B is called $\lambda$-presentable if it is a $\lambda$-presentable object of the comma category A/$\lambda$-presentable morphisms are precisely the pushouts of morphisms between $\lambda$-presentable objects of C.
@article{TAC_2004_12_a11, author = {Michel Hebert}, title = {K-purity and orthogonality}, journal = {Theory and applications of categories}, pages = {355--371}, publisher = {mathdoc}, volume = {12}, year = {2004}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2004_12_a11/} }
Michel Hebert. K-purity and orthogonality. Theory and applications of categories, Tome 12 (2004), pp. 355-371. http://geodesic.mathdoc.fr/item/TAC_2004_12_a11/