Show[
ContourPlot3D[x^2+y^2+z^2==1,{x,-2,2},{y,-2,2},{z,-2,2}, Mesh->None] (* EnhetsSfären*),
ContourPlot3D[x+y-z,{x,-2,2},{y,-2,2},{z,-2,2},Contours->10, Mesh->None (* Nivåyteplanen *)]
]