## § Connectedness in terms of continuity

This was a shower thought.
- We usually define a topological space $X$ as connectediff there are disjoint open sets $U, V$ such that $U \cup V = X$. Sincethey are disjoint, we have that $U \cap V = \emptyset$.
- An alternative way of stating this is to consider two colors
`C = {red, blue }`

withthe discrete topology. - We use the discrete topology on
`C`

since we want the twocolors to be "separate". - Now, a space $X$ is connected iff there is a continuoussurjective function $f: X \rightarrow C$. That is, we can color the whole spacecontinuously with both colors.

This is equivalent to the original definition by setting $U = f^{-1}(red)$
and $V = f^{-1}(blue)$:
- Pre-images of a function must be disjoint. Hence, $U \cap V = \emptyset$.
- Preimages of $red$ and $blue$ must be open sets since $\{red\}$ and $\{blue\}$are open and $f$ is continuous: continuous functions have pre-images of opensets as open. Hence $U$ and $V$ are open.
- Since $f$ is surjective, we must have that the pre-images cover the entire set $X$.Hence $U \cup V = X$.

I find this to be appealing, since it's intuitively obvious to me that if a space
is disconnected, I can color it continuously with two colors, while if a space
is connected, I should be unable to color it continuously with two colors ---
there should be a point of "breakage" where we suddenly switch colors.