Solution (source code)

= Solution
{c}

Take
$$
\boxed{g(x)=-x.}
$$
It is <continuous> for the <Euclidean metric>, since $|g(x)-g(y)|=|x-y|$. But the basic <open set> $[0,1)$ of the target <Sorgenfrey line> has <preimage>
$$
g^{-1}([0,1))=(-1,0].
$$
This is not <open> in the source <Sorgenfrey line>: every basic <neighbourhood> of $0$ contains positive points. Thus $g$ is not <continuous> for the <lower limit topology>.