jpegmode
%quadrillage marks
400 setheight

-10 8 setxrange
-5.5 14.5 setyrange

%% le plan de base
/P1 {-9 -3} def
/P2 {4 -5} def
/P3 {8.5 0} def

/a {-6 4.5 0} def    
/b {6 4.5 0} def    
/c {6 -4.5 0} def    
/d {-6 -4.5 0} def    
/s {0 3 11.4} def
/s' {s pop 0} def
/y {2 3 div s pop c pop ABpoint 0} def
/x {-1 0 0} def

/alpha 30 def
/beta 165 def
/vect_I {alpha cos alpha sin .5 mulv} def
/vect_J {beta cos beta sin .9 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 /S /S' /X /Y] 
[a b c d s s' x y] {xyz2xy} capply
mapnp

S S' Y paral S C interdroite /Y' defpoint
S' X C D interdroite /D' defpoint
S S' X paral S D' interdroite /X' defpoint

X Y A D interdroite /A1 defpoint
X Y B C interdroite /A2 defpoint
X' Y' S D interdroite /A3 defpoint

/fillstyle {.9 setgray fill} def
[A1 A2 Y' A3] polygone*

gsave
   orange
   .8 setlinewidth
   mixte
   [S' C] ligne
   [S' D' S] ligne
grestore

/dotscale {2 dup} def
[S' X Y Y' X'] {times} plot

1.2 setlinewidth
[A D C S] ligne
[A S D] ligne

gsave
   .8 setlinewidth
   pointilles
   [A B C] ligne
   [B S S'] ligne
   [Y Y'] ligne
   [X X'] ligne
grestore

2 setlinewidth
[-12 P2 P1 xdpoint P2 P3] ligne


12 setfontsize
setTimesItalic
   (A) A dltext   
   (B) B urtext	  
   (C) C drtext	  
   (D) D dltext	  
   (S) S urtext   
   (s) S' dltext   
   (X) X dltext   
   (Y) Y drtext   
   (H) P2 (0 7) ultext