-5 3 setxrange
-1 5 setyrange

200 setwidth
/M {-3 4} def

/a M pop def
/b M exch pop def

traceaxes
axesarrow

M dashpoint
18 setfontsize

/arrowscale {2 2} def
/arrowangle -10 def
3 0 O M 1 (<-) tripointarcarrow

1 setlinewidth
[O M] ligne

setTimesItalic
   (M) M ultext
   (a) a 0 dctext
   (b) 0 b brtext
   (O) O dltext
   (r) O M milieu urtext
setSymbol
   (q) 45 O 1 cpoint urtext