# HG changeset patch # User Benedikt Fluhr # Date 1445696033 -7200 # Sat Oct 24 16:13:53 2015 +0200 # Node ID 2974fa163cd17312596a9027d8490f7cf29d826b # Parent f832c5223a7dfc0ff3b027a3144b03e615cd916a Added remark about surjectivity of hom(_, A) diff --git a/06_fromSetsToAlgebras.md b/06_fromSetsToAlgebras.md --- a/06_fromSetsToAlgebras.md +++ b/06_fromSetsToAlgebras.md @@ -98,6 +98,17 @@ $1_{m(1)} \in \mathfrak{a} \subset \mathfrak{m}$ is mapped to $1 \in \Z / p \Z$ under $\hom(m, \Z / p \Z)$. +* *Remark.* +From a discussion similar to that of the previous lemma and example +we can conclude that for sets $K$ and $L$ with $L$ non-empty, the map +from $\hom(L, K)$ to +$\hom_{A\text{-algebras}} (\hom(K, A), \hom(L, A))$ +induced by $\hom(\_, A)$ is surjective if and only if all +ideals^[which are prime necessarily] $\mathfrak{p}$ of $\hom(K, A)$, +with $\hom(K, A) / \mathfrak{p} \cong A$ as $A$-algebras, +are of the form +$\set{c}{\hom(K, A)}{c(k) = 0}$ for some $k \in K$. + * **Lemma.** $\hom(\_, A)$ is continuous as a functor from the opposed category of sets to the category of $A$-algebras.