Separation axioms
<a href="//commons.wikimedia.org/wiki/User:Bijay_chaurasia" class="mw-redirect" title="User:Bijay chaurasia">Bijay chaurasia</a>
2016-11-11
Based on an image by <a href="//commons.wikimedia.org/wiki/User:Toby_Bartels" title="User:Toby Bartels">Toby Bartels</a>. See <code><a rel="nofollow" class="external free" href="http://tobybartels.name/copyright/">http://tobybartels.name/copyright/</a></code>.