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  • 1 University of Tartu, Ülikooli 18, 50090 Tartu, Estonia
  • | 2 University of Tartu, Ülikooli 18, 50090 Tartu, Estonia
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We prove that in the category of firm acts over a firm semigroup monomorphisms co-incide with regular monomorphisms and we give an example of a non-injective monomorphism in this category. We also study conditions under which monomorphisms are injective and we prove that the lattice of subobjects of a firm act over a firm semigroup is isomorphic to the lattice unitary subacts of that act.

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