-4 2 setxrange
-5 5 setyrange
20 setxunit

/A {-3 3} def
/B {-3 -3} def
/C {-1 3 sqrt} def
/D {-1 -6 3 sqrt add} def

/arrowscale {.8 dup} def

tracerepere
marks
[A O B] dup ligne dashpoints
[C D] points
gsave
   .5 setlinewidth
   O C 20 Arc
grestore
pointilles
[A C D B] ligne


setTimesItalic
   (O) O drtext
   (A) A ultext
   (B) B dltext
   (C) C uctext
   (D) D dctext