profile p x 4 y 1 x -3 y 3 x 3 y 1 x -4
prism pr p 0 0 1
explode pr f
profile pp x 0.5 y 0.5 x -0.5 y -0.5
trotate pp 0 0 0 1 0 0 90
ttranslate pp 4 1 0.25
mksurface s1 pr_1
mksurface s2 pr_7
mkface f1 s1
mkface f2 s2

featprism pr pp pp 0 1 0 1 1
featperform prism result f1 f2

set square 54.5