Source
-2.5 3 setyrange
-4.5 3.5 setxrange
35 setxunit
.5 .5 setquadrillagestep
quadrillage
/unites {} def
tracerepere
marks
/ymarkstyle {cltext} def

/A {1 -1} def
/D {2.5 .8} def
/B {-4 -1} def
/C {3 2} def

[B C] points
A dashpoint

1.2 setlinewidth
/arg {argc} def
[B .. -3 0 .. -2 .5 .. -1 0 .. -.5 -1 .. 0 -1.5  {right} .. 1 -1 .. 2 0 .. D .. C] draw

.6 setlinewidth
pointilles

setTimesItalic
   (O) O dltext
   (A) A drtext