//default camera {location 0 look_at z}
background {1-z/2}			//equivalent to background {color rgb <1,1,.05>}
union {
	light_source {-5*z 1}	//equivalent to light_source {-5*z color rgb <1,1,1>}
	light_source {5*x 1}		//equivalent to light_source {5*x color rgb <1,1,1>}
	light_source {5*y z}		//equivalent to light_source {5*y color rgb <0,0,1>}
	isosurface {
		function {
			-x*y*z+y*y*z*z+x*x*(y*y+z*z)	//Roman (Steiner) surface
			}
	max_gradient 3
	pigment {rgbf 1-t/3}		//equivalent to pigment {color rgbf <1,1,1,0.67>}
	interior {ior 7/4}}		//1.75
	translate 1.5*z			//to see it from origin
	}