polyline p 0 0 0 5 0 0 5 0 3 3 0 3 3 0 5 0 0 5 0 0 0
mkplane f p
prism s f 0 5 0
explode s f
donly s
offsetparameter 1e-7 c i 
offsetload s 1 
offsetonface s_4 5
offsetperform result

checkprops result -v 441

checknbshapes result -shell 1
