polyline p 0 0 0 4 0 0 4 0 3 3 0 3 2 0 1 1 0 3 0 0 3 0 0 0
mkplane f p
prism s f 0 1 0

set distance 4
offsetparameter 1.e-7 $calcul $type
offsetload s $distance
offsetperform result

checkprops result -v 1188

checknbshapes result -shell 1
