The straight line AB indicates the two sides connecting A and B, and the ray CD indicates that C is not in the head and D is in the head.

Ray AD means that A is not in the early stage, D is in the early stage, and connecting BC means that both sides are not in the early stage.

Draw the A end of AB a little longer, and the D end of CD a little longer, and they will intersect and mark E on the point.

Connect AC, BD, and the intersection is marked with F.

Please adopt