150 setwidth
150 setheight
-1 5 setxrange
-1 5 setyrange

/x 1 def

/A {0 0} def
/B {4 0} def
/C {4 4} def
/M {x 0} def
A B M perp A C interdroite /Q defpoint
A B Q paral B C interdroite /P defpoint

[P Q M] ligne
A B C angledroit
B M Q angledroit
Q P B angledroit
medium setlinewidth
[A B C] polygone

setTimesItalic
   (A) A dltext
   (B) B drtext
   (C) C utext
   (P) P urtext
   (Q) Q ultext
   (M) M dtext