f1(x,y)=x**6+3*y**2*x**4+(3*y**4-4*y**2)*x**2+y**6
#
C=1
set style line 100 lw 0.1 lc rgb "navy"
set pm3d depth hidden ls 100
set ticslevel 0
set nokey
set xrange[-C:C]
set yrange[-C:C]
set samples 50
set isosamples 50
set contour
set cntrparam levels discrete 0.05,0,-0.05,-0.5 
splot -f1(x,y) w pm3d
pause 3
set term pngcairo size 480,480
set out "stool.png"
replot