Theorem. Left/right adjoints preserve (co)/limits [0IGM]

We have

HomC(X, R lim←⁡D)≅HomC(X,lim←⁡RD)\text{Hom}_{\mathcal{C}}(X,\ R\ \varprojlim D) \cong \text{Hom}_{\mathcal{C}}(X, \varprojlim RD)

and

HomD(Llim→⁡X,Y)≅HomD(lim→⁡LX,Y)\text{Hom}_{\mathcal{D}}(L \varinjlim X, Y) \cong \text{Hom}_{\mathcal{D}}(\varinjlim LX, Y)

Proof [local-0]

Only prove right adjoints preserve limits here, left adjoints case is dual.

It basically invokes Hom-functors preserve limits twice

HomC(X, R lim←⁡D)≅  HomD(L X,lim←⁡D)by adjunction  ≅  lim←⁡j HomD(L X,Dj)representable preserves limits  ≅  lim←⁡j HomC(X,R Dj)by adjunction  ≅  HomC(X,lim←⁡RD)representable preserves limits\begin{aligned} \text{Hom}_{\mathcal{C}}(X,\ R\ \varprojlim D) &\cong\;\text{Hom}_\mathcal{D}(L\ X, \varprojlim D) && \text{by adjunction} \\ &\;\cong\;\varprojlim_j\ \text{Hom}_\mathcal{D}(L\ X, D_j) && \text{representable preserves limits} \\ &\;\cong\;\varprojlim_j\ \text{Hom}_\mathcal{C}(X, R\ D_j) && \text{by adjunction} \\ &\;\cong\;\text{Hom}_\mathcal{C}(X, \varprojlim RD) && \text{representable preserves limits} \end{aligned}