The tülle surface is the quartic surface
 |
named by Hauser. Its German name Tülle means "nozzle." It is the union of the two planes 
and 
and the parabolic cylinder 
.
The pairwise intersections of these three smooth components are the x-axis and the two parabolas 
, 
and 
, 
. All three curves have the
same tangent line at the origin.
Although each pair of components meets transversally, the three tangent
planes at the origin have linearly
dependent normals. Thus this union is not a simple
normal crossing divisor.
