4316.sagews

var('x y z')
A=implicit_plot3d(x+y+z==1,(x,-3,3),(y,-3,3),(z,-3,3))
B=implicit_plot3d(x+y+z==0,(x,-3,3),(y,-3,3),(z,-3,3),color='red')
C=plot3d(x^2+y^2,(x,-3,3),(y,-3,3),color='green')
A+B+C