Show that if $Y$ is a topological space, then every map $f:Y \rightarrow X$ is continuous when $X$ has the indiscrete topology.
Proof:
Assume $X$ has the indiscrete topology, $T=\{\varnothing,X\}$.
$f$ is continuous if $f^{-1}(V)$ is an open subset of $X$ whenever $V$ is an open subset of $Y$.
Let $V$ be an open subset of $Y$.
I dont know how to use this to show $f^{-1}(V)$ is an open subset of $X$.