An illustration of the w:Sorgenfrey plane, showing the anti-diagonal in blue and a typical open rectangle in red. The open rectangle meets the anti-diagonal at a single point; such rectangles can be used to show that the anti-diagonal is an uncountable discrete subspace of the Sorgenfrey plane, and hence that separability does not inherit to subspaces.

I, the copyright holder of this work, release this work into the public domain. This applies worldwide. In some countries this may not be legally possible; if so: I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.