Relationships between the number of singularities of plane algebraic curves. Given a plane curve,
 |  |  |
(1)
|
 |  |  |
(2)
|
 |  |  |
(3)
|
 |  |  |
(4)
|
where 
is the class, 
the curve order, 
the number of ordinary
double points, 
the number of cusps, 
the number of inflection
points (inflection points), and 
the number of bitangents.
Only three of these equations are linearly
independent.
