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Are all subcategories of locally finitely presentable categories that are closed under limits and $\lambda$-filtered colimits also locally presentable? For full subcategories the answer is affirmative. Makkai and Pitts proved that in the case $\lambda = \aleph_0$ the answer is affirmative also for all iso-full subcategories, i. e., those containing with every pair of objects all isomorphisms between them. We discuss a possible generalization of this from $\aleph_0$ to an arbitrary $\lambda$.
@article{TAC_2015_30_a40, author = {J. Adamek and J. Rosicky}, title = {On reflective subcategories of locally presentable categories}, journal = {Theory and applications of categories}, pages = {1306--18}, publisher = {mathdoc}, volume = {30}, year = {2015}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2015_30_a40/} }
J. Adamek; J. Rosicky. On reflective subcategories of locally presentable categories. Theory and applications of categories, Tome 30 (2015), pp. 1306-18. http://geodesic.mathdoc.fr/item/TAC_2015_30_a40/