Limits and colimits can be computed point-wise in functor categories, such as the category of simplicial objects of any category. That is, if you have a functor category mathcalCI (I=Delta in your case) and a functor F:PlongrightarrowmathcalCI, in particular, for every object p in P you have a functor Fp:IlongrightarrowmathcalC. Then varinjlimpFp is an object of mathcalCI; that is, a functor IlongrightarrowmathcalC, whose value on objects i in I is
(varinjlimpFp)(i)=varinjlimp(Fp(i)).
This is true as far as the colimit on the right exists for every object i in I. An analogous statement applies for limits in functor categories.
For limits, you can find the result in MacLane, "Categories for the working mathematician", chapter V, section 3, theorem 1 (see at the end of the proof also). For colimits, see "Sheaves in geometry and logic: a first introduction to topos theory", by Saunders Mac Lane,Ieke Moerdijk, p.40.
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