Bretzel2 Implicit Surface

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bretzel2
bretzel2 implicit 1
Bretzel2 Implicit Surface.

f(x,y,z):==((x^2*(1-x^2)-y^2)^2+0.5*z^2-f*(1+b*(x^2+y^2+z^2))

where b:=1 and f:=0.025. (these values will create a surface similar to the above.