Definition 4.5 (Limit preserving / reflecting / creating). Let F:CD be a functor.

  • (a)
    We say F preserves limits of shape J if, given D:JC and a limit cone (L,(λj|jobJ)) for it, (FL,(Fλj|jobJ)) is a limit for FD:JD.
  • (b)
    We say F reflects limits of shape J if given D:JC, any cone over D which maps to a limit cone in D is a limit in C.
  • (c)
    We say F creates limits of shape J if, given D:JC and a limit cone (L,(λj|jobJ)) over FD, there exists a cone over D whose image under F is (L,(λj)), and any such cone is a limit in C.