Menelaus's Theorem

Menelaus:=proc() local A,B,C,X,Y,Z,L,m,b:

L:=y-m*x-b:   X:=Pt(Le(B,C),L):   Y:=Pt(Le(A,C),L):   Z:=Pt(Le(A,B),L):

ItIsZero(DeSq(B,X)*DeSq(C,Y)*DeSq(A,Z)   -   DeSq(C,X)*DeSq(A,Y)*DeSq(B,Z)):

end: