-1 7 setxrange
-1 5 setyrange

/x 4 def

/A {0 0} def
/B {6 0} def
/M {x 0} def
/P {0 x} def
/N {x dup} def
/Q {6 6 x sub} def
/R {x 6 x sub} def

1 setlinewidth
[A P N R Q B] ligne

pointilles
[M N] ligne
continu
1.7 setlinewidth
[A B] ligne

setTimesItalic
   (A) A dltext
   (B) B drtext
   (P) P ultext
   (Q) Q urtext
   (N) N urtext
   (M) M dtext
   (R) R dltext