Set M of real numbers with the interior point a and an ε-neighbourhood of a fitting in M.
<a rel="nofollow" class="external text" href="http://kulla.me/">Stephan Kulla</a> (<a href="//commons.wikimedia.org/wiki/User:Stephan_Kulla" title="User:Stephan Kulla">User:Stephan Kulla</a>)
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>