TITLE: How can $4$ points in the plane be vertices of $3$ different quadrilaterals?
QUESTION [5 upvotes]: Four points on the plane are vertices of three different quadrilaterals. How can this happen?

The problem is taken from "Kiselev's Geometry - Book I : Planimetry"
At first, I thought it could be like this :

But, the way diagonals are defined in the book:

Makes me think that the 3 figures I drew, are the same quadrilateral.
How do you think four points on the plane can be vertices of three different quadrilaterals

REPLY [18 votes]: Is this what you mean by three different quadrilaterals?