autocrop
0 15 setxrange
20 setxunit
/vAB {7 -.5} def
/vAD {-1 -5} def
/A {3 3} def
/B {A vAB addv} def
/D {A vAD addv} def
/C {B vAD addv} def

/I {A B milieu} def
/J {D C milieu} def
B J A perp B J interdroite /H defpoint
D I A H interdroite /M defpoint

.7 setlinewidth
[A B C D] polygone
%[A B C D I J H M] {times2} plot

A H 1.5 trait
B J 1.2 trait
[H D I] ligne
A H B angledroit

setTimesItalic
   (A) A urtext
   (B) B crtext
   (C) C drtext
   (D) D dltext
   (I) I urtext
   (J) J drtext
   (H) H (3 0) crtext
   (M) M (0 3) uctext