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lemma. Iso [kostecki2011introduction, 2.4] [tt-000E]
✍️source

    An iso arrow is always monic and epic. However, not every arrow which is monic and epic is also iso.

    proof. 

      The diagram commutes for the iso arrow \(f\), thus

      • \(g = h\) i.e. \(f\) is monic,
      • \(k = l\) i.e. \(f\) is epic.