Let(A=[-x1,0], B=[x1,0], C=[x2,x3], D=[0,0], E=[x4,x5], F=[x6,x7]):
Trisectior := Theorem(
    [arbitrary(A,B,C), midpoint(A,B,D), midpoint(C,D,E), 
     intersection(A,E,B,C,F)], [3*x6-2*x2-x1, 3*x7-2*x3], [x4,x5,x6, x7]);
