-2.5 3.5 setxrange
-1 3.5 setyrange
50 setxunit
50 setyunit

/A {0 0} def
/B {3 0} def
/C {3 3} def
/D {0 3} def
/P {1 0} def
/Q {1 3} def
/R {0 1} def
/S {1 1} def
/T {P R C D interdroite} def

[A B C D] polygone
[P B D T] polygone
[A P Q D] polygone

/fillstyle {.9 setgray fill} def
[A P Q D] polygone*

/fillstyle {.1 setgray continu hachure} def
[A P R] polygone* 

/fillstyle {.1 setgray pointilles hachure} def
[T P Q] polygone*
[B D] ligne
[R S] ligne
[B P] (->) ligne
(A) A [1.5 dup] dltext
(B) B [1.5 dup] drtext
(C) C [1.5 dup] urtext
(D) D [1.5 dup] uctext
(Q) Q [1.5 dup] uctext
(P) P [1.5 dup] dctext
(R) R [1.5 dup] dltext
(S) S [1.5 dup] drtext
(T) T [1.5 dup] ultext

<latex>
$a$
</latex>
0.5 -0.3 [1.8 dup] uctexlabel

<latex>
$b$
</latex>
0.95 1.5 [1.8 dup] crtexlabel

<latex>
$b$
</latex>
2.95 1.5 [1.8 dup] crtexlabel

<latex>
$\rm{Abb}.\,1$
</latex>
1.2 -1 [2.0 dup] ultexlabel