autocrop
/r 4 def
/A {r neg 0} def
/B {r 0} def
/D {0 r} def

A dupp -40 dir addv
O r interdroitecercle
popp
/C defpoint

[A B] ligne
[D O] ligne
[A C] ligne
D O A angledroit
A C B angledroit
C A O 1 tripointarc
B C D 1 tripointarc
D B O 1 (=) tripointarc
O B C 1 tripointarc
C D B 1 tripointarc

1.2 setlinewidth
O r cercle
[B D C] polygone

10 setfontsize
setTimes
   (40°) -20 A 1.5 cpoint cctext
   (40°) -65 D 1.5 cpoint cctext
   (45°) 160 B 1.5 cpoint cctext
   (45°) 65 C 1.5 cpoint cctext
   (50°) 205 B 1.5 cpoint cctext
setTimesItalic
   (A) A cltext
   (B) B crtext
   (D) D uctext
   (C) C drtext
   (O) O dltext
<tex>
$\cal C$
</tex>

135 O r .5 add cpoint cctexlabel