Let ,
, and
be tetrahedra in projective three-space
. Then the tetrahedra are said to be desmically related if
there exist constants
,
, and
such that
A desmic surface is then defined as a quartic surface which can be written as
for desmically related tetrahedra ,
, and
. Desmic surfaces have 12 ordinary
double points, which are the vertices of three tetrahedra in three-space (Hunt
1996).