法線が離れたところにある面を取得する方法はありますか。

(
theObj = Teapot segs:10 --create ateapot
convertToMesh theObj --convert to EMesh
theMeshCount = theObj.numfaces --get the number of faces in the object
selArray = #() --init. an array to collect faces
for f = 1 to theMeshCount do --loop through all faces
(
  in coordsys (inverse (viewport.GetTM())) theFN = getFaceNormal theObj f
  if theFN.z < 0 then append selArray f -- if Z is negative, add to array
)
setFaceSelection theObj selArray --set the face selection in the EMesh
max modify mode --go to modify mode
select theObj --select the mesh
subObjectLevel = 3 --go to Face SO level
modPanel.addModToSelection (deleteMesh()) --add a delete mesh, preserving the SO selection
)