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The definition of a functor $F$ between two categories $\mathcal{C}$ and $\mathcal{D}$ says that:

  1. If $f$ is a morphism between objects $A,B \in \mathcal{C}$ then $F(f)$ is a morphism between $F(A),F(B)$.
  2. If $f: A \to B$ and $g: B \to C$ then $F(g \circ f) = F(g) \circ F(f)$.
  3. For each object $A$, $F(\text{Id}_A) = \text{Id}_{F(A)}$.

Is there a standard name for a mapping that satisfies (1) and (2) but not (3)? In other words, a functor without preserving identities?

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  • $\begingroup$ Do you have a specific context in mind? $\endgroup$
    – FShrike
    Commented Aug 5 at 18:17
  • $\begingroup$ Yes, I am working with interpolation functors and compatible couples of Banach spaces. $\endgroup$ Commented Aug 5 at 18:33

1 Answer 1

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It's called a semifunctor (this is the natural notion of morphism between semicategories).

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