-2 4 setxrange
-2 4 setyrange
quadrillage

tracerepere
marks

/A {0 -1} def
/B {2 3} def
/I {A B milieu} def
/J {-1 2} def
/K {-5 4 div 1} def

A B diamcercle /cerc defcercle

gsave
   pointilles
   [A B] 
   dup points
   ligne
grestore

[I J K] {times2} plot


.8 setlinewidth
cerc cercle

setTimesItalic
   (O) O dltext
   (A) A dltext
   (B) B urtext
   (I) I bltext
   (J) J cltext
   (K) K cltext