autocrop
-11 21 setxrange
-11 21 setyrange
10 setxunit
10 setfontsize
/x 2 def
/A {0 10} def
/D {0 0} def
/C {10 0} def
/B {10 10} def

/I {x 10} def
/J {0 10 x sub} def
/K {10 x sub 0} def
/L {10 x} def


1 setlinewidth
/fillstyle {.8 setgray fill} def
[A B C D] polygone*
.7 setlinewidth
/fillstyle {1 setgray fill} def
[I J K L] polygone*

[
A I J A L C C K
]
{1 marked} dapply
[
I B B L K D D J
]
{2 marked} dapply
[J A I I B L L C K K D J] {angledroit} 6 6 Apply

setTimesItalic
   (A) A ultext
   (B) B urtext
   (C) C drtext
   (D) D dltext
   (I) I uctext
   (J) J cltext
   (K) K dctext
   (L) L crtext

-15 0 translate
[A J] (<->) ligne
[J D] (<->) ligne
   (x) J D milieu cltext
setTimes
   (0,1) A J milieu cltext