Let be a primitive form, and let
its Hessian. Recall that we write
if F has a triple root in . Then
- if and only if F has at least a double root
in , and if this is the case all the roots of F are in fact in
- if and only if .
- If and , then if and only if
. If then .
- If then we have the following:
If , then .
If but , then .
If and , then there exists such that
, and then .