Let(A=[0,0], B=[x1,0], C=[x2,x3], D=[x4,x5], H=[x6,x7], F=[x8,0]):
Menelaus := Theorem(
    [arbitrary(A,B,C), collinear(A,C,D), collinear(B,C,H),
     intersection(A,B,D,H,F)], sdistance(B,H)*sdistance(C,D)*sdistance(A,F) 
     - sdistance(H,C)*sdistance(D,A)*sdistance(F,B), [x5, x7, x8]);
