%% code obsolete, desole
-5 5 setxrange
-3 5 setyrange

quadrillage

/A {1 0} def
/B {2 0} def
/C {4 0} def
/D {-4 0} def
/E {0 2} def
/F {-2 0} def
/G {1 -3} def
O A B C D 5 points

.8 setlinewidth

A B milieu .5 180 0 sarc
A 1 0 180 sarc
B 2 180 0 sarc
O 4 0 180 sarc

setTimesItalic
   (O) O ultext