%@AUTEUR:Guillaume Connan

prologues:=2;

verbatimtex
%&latex
\documentclass{article}
\usepackage[upright]{fourier}
\begin{document}
etex

input geometriesyr16

figure(0,0,6cm,6cm);
pair M,N,P,O;
path cc;

O=(3cm,3cm);

drawarrow (3cm,0)--(3cm,6cm);drawarrow (0,3cm)--(6cm,3cm);

cc=cercles(O,2cm);
trace grille(0.5) withcolor .5white;

trace cc withpen pencircle scaled 1.1bp withcolor 0.5white;

N=pointarc(cc,240);
P=pointarc(cc,120);

dotlabel.ulft(btex $\frac{2\pi}{3}$ etex,P);
dotlabel.llft(btex $\frac{4\pi}{3}$ etex,N);
dotlabel.lrt(btex {\footnotesize $-\frac{1}{2}$} etex,(2cm,3cm));

draw N--P dashed evenly withpen pencircle scaled 1.2bp withcolor red;

fin;

end