### Steiner Relative

This surface can be transformed into Steiner's Roman Surface or
Cross-Cap Surface by a complex projective change of coordinates,
but not by a real transformation. It has two pinch points and
three double lines, and, unlike the Roman or Cross-Cap, is not compact
in any affine neighborhood.
Polynomial:

x^2*y^2-x^2*z^2+y^2*z^2-x*y*z=0

Here is the PoV3-source I used

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