-1 6 setyrange

%% rayon du grand cercle
/r 4 def

%% angle definissant le point N
/alpha 60 def

/A {r neg 0} def
/B {r 0} def
/I {A O milieu} def
/c1 {O r} def
/c2 {I r 2 div} def
alpha c2 cpoint /N defpoint
A N c1 interdroitecercle /M defpoint 
popp

/T1 {M O M perp} def
/T2 {N I N perp} def

.4 setgray

180 0 c1 Cercle
180 0 c2 Cercle
[A B] ligne
[A M O N] ligne

0 setgray
T1 droite
T2 droite
[I N] ligne

N M O .5 (-) tripointarc
O A N .5 (-) tripointarc

N O A .5 (=) tripointarc
M O N .4 (=) tripointarc

I N T2 exchp popp angledroit
O M T1 exchp popp angledroit

<tex>
$$
   {\cal C} _1
$$
</tex>
25 c1 cpoint [1.5 dup] texlabel
<tex>
$$
   {\cal C} _2
$$
</tex>
105 c2 cpoint [1.5 dup] ultexlabel

setTimesItalic
   (O) O dctext
   (I) I dctext
   (A) A dltext
   (B) B drtext
   (M) M urtext
   (N) N uctext
   (T) -5 T2 xdpoint urtext
   (2) indice
   (T) -1 T1 xdpoint urtext
   (1) indice