Function space/Monotone/R/No subspace/Exercise

Show that the subset

${}M={\left\{f:\mathbb {R} \rightarrow \mathbb {R} \mid f{\text{ monotonic}}\right\}}\subseteq \operatorname {Map} \,{\left(\mathbb {R} ,\mathbb {R} \right)}\,$

is not a linear subspace.

Create a solution