| 
autocrop
-10 4 setyrange
-15 5 setxrange
/A {-2 2} def 
/B {2 2} def 
/C {2 -2} def 
/D {-2 -2} def 
D point
[A B C D] polygone
[A C] ligne
[B D] ligne
/C1 {D D A distance} def
/C2 {C A C distance} def
/E {-90 C1 cpoint} def
90 270 C1 Cercle
135 225 C2 Cercle
gsave
   newpath
      E smoveto
      270 90 C1 Cercle_
      135 225 C2 Cercle_
   clip
   hachure
grestore
pointilles
[D E] ligne
setTimesItalic
   (A) A uctext
   (B) B urtext
   (C) C drtext
   (D) D drtext
   (E) E drtext
<tex>
${\cal C}_1$
</tex>
130 C1 cpoint [1.3 dup] ultexlabel
<tex>
${\cal C}_2$
</tex>
170 C2 cpoint [1.3 dup] drtexlabel
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