Date: May 7, 2013 12:46 PM
Author: Joe Niederberger
Subject: Re: Based on the quadrilateral tree

>The restrictive definition allows its advocates to be certain that an isosceles trapezoid is not a parallelogram.

*Absolutely* certain.

It would be nice if these things could be taught in way that lets the students see when things are, for lack of a better term, "conventional", and when they are not.
This reminds me of the discussion a while back about the conventionality of the area measure of the unit square,
which, it became clear, is not universally recognized as such.

Joe N