Question 199295
<pre><font size = 4 color = "indigo"><b>
A square and a single diagonal will do:

{{{drawing(400,400,-1,2,-1,2, rectangle(0,0,1,1),  
locate(0,0,A), locate(1,0,B), locate(1,1.15,C), locate(0,1.15,D),
triangle(0,0,1,1,1,0) )}}}

B and D are even vertices because 2 line segments issue from 
each and 2 is an even number.  A and C are odd vertices because
3 line segments issue from each of those and 3 is an odd number.

Edwin</pre>