400 setwidth
400 setheight
-2 16 setxrange
-3.5 14.5 setyrange

/fillstyle {.9 setgray fill} def
jpegmode

/l 8 def

/a {0 l l} def       /e {0 l 0} def       /i {5 0 l} def        
/b {l l l} def       /f {l l 0} def       /j {l 5 l} def        
/c {l 0 l} def       /g {l 0 0} def       /k {l 0 4} def       	
/d {0 0 l} def       /h {0 0 0} def       /m {l 2 div 0 0} def  

/vect_I {-10 cos -10 sin} def
/vect_J {35 cos 35 sin .8 mulv} def
/vect_K {0 1} def

/xyz2xy {
3 dict begin
   /z exch def
   /y exch def
   /x exch def
   vect_I x mulv
   vect_J y mulv
   vect_K z mulv
   addv addv
end
} def

[/A /B /C /D /E /F /G /H /I /J /K /M] 
[a b c d e f g h i j k m] {xyz2xy} capply
mapnp

%% intersection no 1
A C I J interdroite /A1 defpoint
M C I K interdroite /A2 defpoint
A A1 M paral 
H E interdroite /A3 defpoint

%% trace intersection 1
/fillstyle {.9 setgray fill} def
mixte [A A1 A2 M A3] polygone* continu

1 setlinewidth
[A D I J B A] ligne
[D H G F B] ligne
[I K J] ligne
[K G] ligne

gsave
   pointilles
   [A E H] ligne
   [E F] ligne
grestore

12 setfontsize
setTimesItalic
   (A) A ultext   (F) F brtext   (J) J ultext
   (B) B urtext   (G) G drtext   (K) K drtext
   (D) D ultext   (H) H dltext   (M) M dctext
   (E) E urtext   (I) I uctext