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

set distance 1
offsetparameter 1.e-7 $calcul $type
offsetload s $distance
explode s f
offsetonface s_4 3
offsetperform result

checkprops result -v 60

checknbshapes result -shell 1
