Relations are used to define attributes such as tangency, parallelism, perpendicularity, and concentricity. The curve has a unique vertex at the point of tangency with its defining circle. The two diagonals and the two tangency chords are concurrent. As "n" increases the order of self intersection increases&colon; transverse crossing, ordinary tangency, etc. Thus, the intersection degree is two; it is an ordinary tangency. Such a point of contact must be a tangency. This is also known as the flow tangency condition. The property of tangency is defined as follows. The two points of tangency are also double points. There are two types of tangency&colon; internal and external. The set of all such tangency points is called the firm's "expansion path". The relationship between transversality and tangency is clearest when formula 19.