- #1
Mandelbroth
- 611
- 24
I think this looks like a homework problem, so I'll just put it here.
Demonstrate that, for any index category ##\mathscr{J}## and any diagram ##\mathcal{F}:\mathscr{J}\to\mathbf{Sets}##,
$$\varprojlim_{\mathscr{J}}A_j=\left\{a\in \prod_{j\in \operatorname{obj}( \mathscr{J})}A_j~\vert~(i,k\in\operatorname{obj}(\mathscr{J}),~a_i\in A_i,~a_k\in A_k, \text{ and } \phi_{ik}\in \hom_{\mathscr{J}}(i,k))~\implies~a_k=\mathcal{F}(\phi_{ik})(a_i) \right\}=A$$
along with the obvious projections, which I'll denote ##l_i: A\to A_i##.
I don't know how to make diagrams in TeX, so I'll just link to the universal property.
Suppose ##W## has morphisms ##w_i: W\to A_i## that satisfy ##w_k=\mathcal{F}(\phi_{ik})\circ w_i##. We wish to show the existence of a unique morphism ##w: W\to A## such that ##w_i=l_i\circ w##.
My thought is that both ##W## and ##A## clearly map into the product ##\prod A_j##. We even have the unique map from ##A## to ##\prod A_j##, set inclusion, satisfying the universal property for the product. However, I don't know how to proceed. Any nudges in the right direction would be helpful. Thank you!
Homework Statement
Demonstrate that, for any index category ##\mathscr{J}## and any diagram ##\mathcal{F}:\mathscr{J}\to\mathbf{Sets}##,
$$\varprojlim_{\mathscr{J}}A_j=\left\{a\in \prod_{j\in \operatorname{obj}( \mathscr{J})}A_j~\vert~(i,k\in\operatorname{obj}(\mathscr{J}),~a_i\in A_i,~a_k\in A_k, \text{ and } \phi_{ik}\in \hom_{\mathscr{J}}(i,k))~\implies~a_k=\mathcal{F}(\phi_{ik})(a_i) \right\}=A$$
along with the obvious projections, which I'll denote ##l_i: A\to A_i##.
Homework Equations
I don't know how to make diagrams in TeX, so I'll just link to the universal property.
The Attempt at a Solution
Suppose ##W## has morphisms ##w_i: W\to A_i## that satisfy ##w_k=\mathcal{F}(\phi_{ik})\circ w_i##. We wish to show the existence of a unique morphism ##w: W\to A## such that ##w_i=l_i\circ w##.
My thought is that both ##W## and ##A## clearly map into the product ##\prod A_j##. We even have the unique map from ##A## to ##\prod A_j##, set inclusion, satisfying the universal property for the product. However, I don't know how to proceed. Any nudges in the right direction would be helpful. Thank you!