Let M be a class of (mono)morphisms in a category A. To study mathematical notions, such as injectivity, tensor products and flatness, one needs to have some categorical and algebraic information about the pair (A,M). In this paper we take A to be the category Act-S of S-acts, for a semigroup S, and Msd to be the class of strongly s-dense monomorphisms and study the categorical properties, such as limits and colimits, of this class.
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