General Topology
http://www.maa.org/taxonomy/term/41819/0
enTopology Explains Why Automobile Sunshades Fold Oddly
http://www.maa.org/programs/maa-awards/writing-awards/topology-explains-why-automobile-sunshades-fold-oddly
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Award: George Pólya</p>
<p>Year of Award: 2010</p>
<p>Publication Information: College Mathematics Journal, vol. 40, no. 2, March 2009, pp. 93-98</p>
<p>Summary: In this article the authors examine "automatic folding" sunshades that coil up when not in use. From the authors' experience, it seems impossible simply to fold such a sunshade in half (i.e. coil it into exactly two loops.) The object here is to figure out how many loops can appear in the coil and to understand why.</p></div></div></div>Euler's Theorem for Generalized Quadrilaterals
http://www.maa.org/programs/faculty-and-departments/classroom-capsules-and-notes/eulers-theorem-for-generalized-quadrilaterals
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><I>The sum of squares of the sides of quadrilateral is equal to the sum of the squares of the diagonals plus 4 times the square of the segment joining the midpoints of the diagonals.</I></div></div></div>