# Theorem from "Charles R. Jolivette" <crjolly@clover.net>
# Date: Sun, 13 Dec 1998 21:02:08 -0500
Let(A=[x1,0], D=[x2,0], B=[x3, x4], C=[x5,x4], E=[x6, x7], F=[x8, x9]):
Trapezoid := Theorem(
    [arbitrary(A,B,C), parallel(A,D,B,C), midpoint(A,C,E), midpoint(B,D,F)], 
    [parallel(E,F,A,D), parallel(E,F,B,C),
     (4*sdistance(E,F)-sdistance(A,D)-sdistance(B,C))^2
     -4*sdistance(A,D)*sdistance(B,C)], [x6, x7, x8, x9] );
